May 06, 2020 Install Katoolin3 in Ubuntu 20.04 LTS. I have tested Katoolin3 in Ubuntu 20.04 LTS server edition. However, It should work on other Ubuntu versions and derivatives. Katoolin3 requires the following prerequisites in your Ubuntu system. Firefox for developers currently resides in Firefox Aurora builds: “Ubuntu Mozilla Daily Build Team” team.It should be noted that: 'Firefox Developer Edition replaces the Aurora channel in the Firefox Release Process.Like Aurora, features will land in the Developer Edition every six weeks, after they have stabilized in Nightly builds.'
- The browser made for developers. All the latest developer tools in beta, plus experimental features like the Multi-line Console Editor and WebSocket Inspector. A separate profile and path so you can easily run it alongside Release or Beta Firefox. Preferences tailored for web developers: Browser and remote debugging are enabled by default, as are the dark theme and developer toolbar button.
- And then if you still want gnome-software install it as a deb, but that is then not Ubuntu branded but the stock gnome-software. This is what Mint has to prevent snaps, but since Ubuntu repositories are available you can just remove that on Mint and then install all snaps you want.
Firefox is a popular open source graphical web browser from Mozilla.
Firefox can be installed with the firefox package.
Other alternatives include:
- Firefox Developer Edition — for developers
- https://www.mozilla.org/firefox/developer/ firefox-developer-edition
- Firefox Extended Support Release — long-term supported version
- https://www.mozilla.org/firefox/organizations/ firefox-esrAUR or firefox-esr-binAUR
- Firefox Beta — cutting-edge version
- https://www.mozilla.org/firefox/channel/desktop/#beta firefox-betaAUR or firefox-beta-binAUR
- Firefox Nightly — nightly builds for testing (experimental features)
- https://www.mozilla.org/firefox/channel/desktop/#nightly firefox-nightlyAUR
- Firefox KDE — Version of Firefox that incorporates an OpenSUSE patch for better KDE integration than is possible through simple Firefox plugins.
- https://build.opensuse.org/package/show/mozilla:Factory/MozillaFirefox firefox-kde-opensuseAUR
- On top of the different Mozilla build channels, a number of forks exist with more or less special features; see List of applications#Gecko-based.
A number of language packs are available for Firefox, other than the standard English. Language packs are usually named as
languagecode can be any language code, such as de, ja, fr, etc.). For a list of available language packs see firefox-i18n for firefox,firefox-developer-edition-i18n for firefox-developer-edition and firefox-nightly- for firefox-nightlyAUR.
Firefox is well known for its large library of add-ons which can be used to add new features or modify the behavior of existing features. Firefox's 'Add-ons Manager' is used to manage installed add-ons or find new ones.
For instructions on how to install add-ons and a list of add-ons, see Browser extensions.
Adding search engines
Search engines may be added to Firefox by creating bookmarks with the
Location field using search URLs completed with %s in place of the query and the
Keyword field completed with user-defined characters:
Searches are performed by pre-pending the search term with the keyword of the specified search engine:
d archwiki will query DuckDuckGo using the search term
Search engines may also be added to Firefox through add-on extensions, see this page for a list of available search tools and engines.
A very extensive list of search engines can be found at the Mycroft Project.
Also, you can use the add-to-searchbar extension to add a search to your search bar from any web site, by simply right clicking on the site's search field and selecting Add to Search Bar...
Install the firefox-extension-arch-searchAUR package to add Arch-specific searches (AUR, wiki, forum, packages, etc) to the Firefox search toolbar.
Support for all plugins, including Flash Player, was removed in Firefox 85.
Firefox exposes a number of configuration options. To examine them, enter in the Firefox address bar:
Once set, these affect the user's current profile, and may be synchronized across all devices via Firefox Sync. Please note that only a subset of the
about:config entries are synchronized by this method, and the exact subset may be found by searching for
about:config. Additional preferences and third party preferences may be synchronized by creating new boolean entries prepending the config value with services.sync.prefs.sync. To synchronize the whitelist for the extension NoScript:
noscript.sync.enabled must be set to
true to synchronize the remainder of NoScript's preferences via Firefox Sync.
Firefox also allows configuration for a profile via a
user.js file: user.js kept in the profile folder, usually
~/.mozilla/firefox/xxxxxxxx.default/. For a useful starting point, see e.g custom user.js which is targeted at privacy/security conscious users.
One drawback of the above approach is that it is not applied system-wide. Furthermore, this is not useful as a 'pre-configuration', since the profile directory is created after first launch of the browser. You can, however, let firefox create a new profile and, after closing it again, copy the contents of an already created profile folder into it.
Sometimes it may be desired to lock certain settings, a feature useful in widespread deployments of customized Firefox. In order to create a system-wide configuration, follow the steps outlined in Locking preferences:
/usr/lib/firefox/mozilla.cfg (this stores the actual configuration):
Please note that the first line must contain exactly
//. The syntax of the file is similar to that of
Firefox uses FFmpeg for playing multimedia inside HTML5
<video> elements. Go to video-test page or audio-test page to check which formats are actually supported.
The factual accuracy of this article or section is disputed.
Firefox uses PulseAudio for audio playback and capture. For sound to work, you need to install the pulseaudio package.
In case, for whatever reason, PulseAudio is not an option for you, you can use apulse instead. To make this work, it is necessary to exclude
/dev/snd/ from Firefox' sandboxing by adding it to the comma-separated list in
/dev/snd/is important, otherwise apulse will report 'Permission denied' errors.
If you have no audio even when using apulse, try adding
Widevine is a digital rights management tool that Netflix, Amazon Prime Video, and others use to protect their video content. It can be enabled in Preferences > General > Digital Rights Management (DRM) Content. If you visit a Widevine-enabled page when this setting is disabled, Firefox will display a prompt below the address bar asking for permission to install DRM. Approve this and then wait for the 'Downloading' bar to disappear, you are now able to watch videos from Widevine protected sites.
Firefox can only play 720p video (or lower) with Widevine, due to not using hardware DRM playback. It is also required that the private mode browsing is disabled, for the window and in the preferences.
Open With extension
- Install Open With add-on.
- Go to Add-ons > Open With > Preferences.
- Proceed with instructions to install a file in your system and test the installation.
- Click Add browser.
- In the dialog write a name for this menu entry and command to start a video streaming capable player (e.g. /usr/bin/mpv).
- (Optional step) Add needed arguments to the player (e.g. you may want
--force-window --ytdlfor mpv)
- Right click on links or visit pages containing videos. Select newly created entry from Open With's menu and if the site is supported, the player will open as expected.
The same procedure can be used to associate video downloaders such as youtube-dl.
Hardware video acceleration
Hardware video acceleration via VA-API is available under Wayland (see Firefox gets VA-API on Wayland) and X.org (see bugzilla X11 implement VAAPI and Phoronix news VA API X11).Note:
- AMDGPU users under linux-hardened may need to rebuild linux-hardened with
CONFIG_CHECKPOINT_RESTORE=ydue to mesarequiring the kcmp syscall.
- Hardware video acceleration on multi-GPU systems is affected by a device selection bug.
- VP8/VP9 decoding is affected by a sandboxing bug. FF84+ users may set
falseto bypass the RDD process.
Before trying VA-API support in Firefox be sure to:
- Install correct VA-API driver for your video card and verify VA-API has been enabled and working correctly, see Hardware video acceleration;
- For Intel graphics, use the i965 driver libva-intel-driver if your hardware supports it.
- The iHD driver intel-media-driver (needed by Broadwell or newer) is currently broken due to sandbox violations caused by the driver (see Bugzilla 1619585). This can be worked around by setting the
0, at the risk of losing sandbox protection.
- Use a compositor that supports hardware acceleration, either:
- WebRender from the new Servo browser engine, which can be enabled as explained in /Tweaks#Enable WebRender compositor. It is enabled by default in GNOME and other DEs .
- Gecko's legacy OpenGL back-end, which can be enabled as explained in /Tweaks#Enable OpenGL compositor;
- Set the following flags in
truein order to enable the use of VA-API with FFmpeg;
falseto disable the internal decoders for VP8/VP9.
falseto disable the remote data decoder process for VP8/VP9. As of Firefox 85 its sandbox blocks VA-API access .
trueto enable hardware VA-API decoding for WebRTC.
- Run Firefox with the following environment variable enabled:
- In Wayland, with
MOZ_ENABLE_WAYLAND=1, see #Wayland.
- In X.org, with
- In Wayland, with
- You can verify that VA-API is enabled by running Firefox with
MOZ_LOG='PlatformDecoderModule:5'environment variable and check in the log output that VA-API is enabled and used (search for the 'VA-API' string) when playing a video for example. Pay attention to these logs as they might indicate that only one of the two possible compositors described before (OpenGL or WebRender) works with VA-API on your particular setup.
- For Intel GPU, the intel_gpu_top utility from package intel-gpu-tools can be used to monitor the GPU activity during video playback for example. For AMD GPU, use radeontop.
- To allow hardware decoding in YouTube, the video codec used must be supported by the hardware. The profiles supported by your GPU can be checked with Hardware video acceleration#Verifying VA-API and the YouTube codecs used can sometimes (if offered by YouTube!) be controlled with the h264ify or enhanced-h264ify extensions. Alternatively, you can install firefox-h264ifyAUR.
Firefox can use system-wide installed Hunspell dictionaries as well as dictionaries installed through its own extension system.
To enable spell checking for a specific language right click on any text field and check the Check Spelling box. To select a language for spell checking to you have right click again and select your language from the Languages sub-menu.
When your default language choice does not stick, see #Firefox does not remember default spell check language.
System-wide Hunspell dictionaries
Install Hunspell and its dictionaries for the languages you require.
Dictionaries as extensions
To get more languages right click on any text field and just click Add Dictionaries... and select the dictionary you want to install from the Dictionaries and Language Packs list.
- To bring the KDE look to GTK apps (including Firefox), install breeze-gtk and kde-gtk-config. Afterwards, go to System Settings and in Appearance > Application Style > Configure GNOME/GTK Application Style… choose 'Breeze'.
- To use the KDE file selection and print dialogs in Firefox 64 or newer, install xdg-desktop-portal and xdg-desktop-portal-kde, then do one of the following:
- Launch firefox with
- For integration with KDE MIME type system, proxy and file dialog, one can use firefox-kde-opensuseAUR variant from AUR with OpenSUSE’s patches applied. Alternatively, integration with MIME types can be achieved by creating a symbolic link to the MIME database
~/.config/mimeapps.listfrom the deprecated
~/.local/share/applications/mimeapps.listthat is used by Firefox. See XDG MIME Applications#mimeapps.list.
- Extensions/add-ons may provide additional integration, such as:
- Browser integration in Plasma: requires plasma-browser-integration and the Plasma Integration add-on.
Tips and tricks
For general enhancements see Firefox/Tweaks, for privacy related enhancements see Firefox/Privacy.
If a dark GTK theme is in use (e.g. Arc Dark), it is recommended to start Firefox with a brighter one (e.g. Adwaita). See GTK#Themes and Firefox/Tweaks#Unreadable input fields with dark GTK themes for more information.
Alternatively, starting with Firefox 68 you can make all the Firefox interfaces and even other websites respect dark themes, irrespective of the system GTK theme and Firefox theme. To do this, set
If Firefox is unable to automatically detect the right value, it will default to 60 fps. To manually correct this, set
layout.frame_rate to the refresh rate of your monitor (e.g. 144 for 144 Hz).
To prevent pages from abusing memory (and possible OOM), we can use Firejail with the
New tabs position
To control where new tabs appears (relative or absolute), use
browser.tabs.insertRelatedAfterCurrent. See  for more information.
Screenshot of webpage
You can Take a Screenshot by either clicking the Page actions button (the three horizontal dots) in the address bar or by right-clicking on the webpage. See  for more information.
As an alternative you can use the screenshot button in the Developer Tools.
More recent versions of Firefox support opting into Wayland via an environment variable.
To make this permanent, see Environment variables#Graphical environment and start Firefox via the desktop launcher like you normally would. To verify it worked check the Window Protocol again.
You may enter
about:support in the URL bar to check the Window Protocol. It should say wayland instead of x11 or xwayland.
Window manager rules
To apply different configurations to Firefox windows, change the WM_CLASS string by using Firefox's
--class option, to a custom one.
To start new Firefox instances, multiple profiles are required. To create a new profile:
Class can be specified when launching Firefox with a not-in-use profile:
Touchscreen gestures and pixel-perfect trackpad scrolling
This article or section is a candidate for merging with Firefox/Tweaks#Enable touchscreen gestures.
To enable touch gestures (like scrolling and pinch-to-zoom) and one-to-one trackpad scrolling (as can be witnessed with GTK3 applications like Nautilus), set the
MOZ_USE_XINPUT2=1environment variable before starting Firefox.
Multiple home pages
To have multiple tabs opened when starting Firefox open a new window and then open the sites you want to have as 'home tabs'.
Now go to Preferences > Home and under Homepage and new windows click the Use Current Pages button.
Alternatively go directly to Preferences > Home and now under Homepage and new windows set the first field to Custom URLs.. and enter the pages you want as new home pages in the following format:
Extension X does not work on some Mozilla owned domains
By default extensions will not affect pages designated by
extensions.webextensions.restrictedDomains. If this is not desired, this field can be cleared (special pages such as
about:* will not be affected).
Firefox startup takes very long
If Firefox takes much longer to start up than other browsers, it may be due to lacking configuration of the localhost in
/etc/hosts. See Network configuration#Local network hostname resolution on how to set it up.
See Font configuration.
Firefox has a setting which determines how many replacements it will allow from fontconfig. To allow it to use all your replacement-rules, change
127 (the highest possible value).
Firefox ships with Twemoji Mozilla font. To use system emoji font set
Firefox has problems with Emoji presentation . Set
0 as workaround.
Setting an email client
Inside the browser,
mailto links by default are opened by a web application such as Gmail or Yahoo Mail. To set an external email program, go to Preferences > Applications and modify the action corresponding to the
mailto content type; the file path will need to be designated (e.g.
/usr/bin/kmail for Kmail).
Outside the browser,
mailto links are handled by the
x-scheme-handler/mailto mime type, which can be easily configured with xdg-mime. See Default applications for details and alternatives.
See Default applications.
Firefox keeps creating ~/Desktop even when this is not desired
~/Desktop as the default place for download and upload files. To change it to another folder, set the
XDG_DESKTOP_DIR option as explained in XDG user directories.
Make plugins respect blocked pop-ups
Some plugins can misbehave and bypass the default settings, such as the Flash plugin. You can prevent this by doing the following:
about:configinto the address bar.
- Right-click on the page and select New > Integer.
- Name it
- Set the value to
The possible values are:
0: Allow all popups from plugins.
1: Allow popups, but limit them to
2: Block popups from plugins.
3: Block popups from plugins, even on whitelisted sites.
Changes to userChrome.css and userContent.css are ignored
To use the middle mouse button to paste whatever text has been highlighted/added to the clipboard, as is common in UNIX-like operating systems, set either
middlemouse.contentLoadURL enabled was the default behaviour prior to Firefox 57.
To scroll on middle-click (default for Windows browsers) set
Backspace does not work as the 'Back' button
According to MozillaZine, the
Backspace key was mapped based on which platform the browser was running on. As a compromise, this preference was created to allow the
Backspace key to either go back/forward, scroll up/down a page, or do nothing.
Backspace go back one page in the tab's history and
Shift+Backspace go forward, set
To have the
Backspace key scroll up one page and
Shift+Backspace scroll down one page, set
1. Setting this property to any other value will leave the key unmapped (Arch Linux defaults to
2, in other words, it is unmapped by default).
Firefox does not remember login information
It may be due to a corrupted
cookies.sqlite file in Firefox's profile folder. In order to fix this, just rename or remove
cookie.sqlite while Firefox is not running.
Open a terminal of choice and type the following:
The profile id is a random 8 character string.
Restart Firefox and see if it solved the problem.
If it did not work, check if there exists a
cookies.sqlite.bak file that you could use to manually restore the cookies.
Cannot enter/leave fullscreen
If Firefox detects an EWMH/ICCCM compliant window manager, it will try to send a WM_STATE message to the root window to request Firefox be made to enter (or leave) full-screen mode (as defined by the window manager). Window managers are allowed to ignore it, but if they do, Firefox will assume the request got denied and propagate it to the end user which results in nothing happening. This may result in not being able to full screen a video. A general workaround is to set the
Related bug reports: Bugzilla 1189622.
Firefox detects the wrong version of my plugin
When you close Firefox, the latter saves the current timestamp and version of your plugins inside
pluginreg.dat located in your profile folder, typically in
If you upgraded your plugin when Firefox was still running, you will thus have the wrong information inside that file. The next time you will restart Firefox you will get that message
Firefox has prevented the outdated plugin 'XXXX' from running on ... when you will be trying to open content dedicated to that plugin on the web. This problem often appears with the official Adobe Flash Player plugin which has been upgraded while Firefox was still running.
The solution is to remove the file
pluginreg.dat from your profile and that is it. Firefox will not complain about the missing file as it will be recreated the next time Firefox will be closed. 
You can try setting
Firefox does not remember default spell check language
The default spell checking language can be set as follows:
about:configin the address bar.
spellchecker.dictionaryto your language of choice, for instance
- Notice that the for dictionaries installed as a Firefox plugin the notation is
en-GB, and for hunspell dictionaries the notation is
When you only have system wide dictionaries installed with hunspell, Firefox might not remember your default dictionary language settings. This can be fixed by having at least one dictionary installed as a Firefox plugin. Notice that now you will also have a tab Dictionaries in Add-ons. You may have to change the order of preferred language for displaying pages in
about:preferences#general to make the spell check default to the language of the addon dictionary.
Related questions on the StackExchange platform: , , 
Related bug reports: Bugzilla 776028, Ubuntu bug 1026869
Some MathML symbols are missing
You need some Math fonts, namely Latin Modern Math and STIX (see this MDN page: ), to display MathML correctly.
Install Firefox Developer Edition On Ubuntu Laptop
In Arch Linux, these fonts are provided by texlive-coreandtexlive-fontsextra, but they are not available to fontconfig by default. See TeX Live#Making fonts available to Fontconfig for details. You can also try other Math fonts. In case you encounter this bug  installing otf-latinmodern-math can help.
Tearing video in fullscreen mode
If you are using the Xorg Intel or Nouveau drivers and experience tearing video in fullscreen mode, try Firefox/Tweaks#Enable OpenGL compositor.
Tearing when scrolling
Try disabling smooth scrolling in Preferences > Browsing.
Firefox WebRTC module cannot detect a microphone
WebRTC applications for instance Firefox WebRTC getUserMedia test page say that microphone cannot be found. Issue is reproducible for both ALSA or PulseAudio setup. Firefox debug logs show the following error:
You can try setting
media.navigator.audio.full_duplex property to
about:config Firefox page and restart Firefox.
This can also help if you are using the PulseAudio module-echo-cancel and Firefox does not recognise the virtual echo canceling source.
Cannot login with my Chinese account
Firefox provides a local service for Chinese users, with a local account totally different from the international one. Firefox installed with the firefox package uses the international account system by default, to change into the Chinese local service, you should install the add-on manager on this page, then you can login with your Chinese account now.
No audio on certain videos when using JACK and PulseAudio
If you are using JACK in combination with PulseAudio and cannot hear any sound on some videos it could be because those videos have mono audio. This happens if your JACK setup uses more than just stereo, but you use normal headphones. To fix this you simply have to connect the
front-center port from the PulseAudio JACK Sink to both
playback_2 ports of the system output.
You can also do this automatically using a script:
Keep in mind that the names for the sink and the ports might be different for you. You can check what your JACK setup looks like with a Patchbay like Catia from cadence.
Geolocation does not work
Recently, Google limited the use of its location service with Arch Linux, which causes the following error when geolocation is enabled on a website:
Geolocation error: Unknown error acquiring position. Region-locked services such as Hulu may display a similar error indicating that your location could not be determined even though you have allowed location services for the site.
To avoid these problems, you can switch to use the Mozilla Location Service. In
about:config change the
geo.provider.network.url setting to:
See FS#65241 for more details.
Right mouse button instantly clicks the first option in window managers
This problem has been observed in i3, bspwm and xmonad.
To fix it, navigate to
about:config and change
- mozillaZine unofficial forums