Firefox Tweaker

What is Firefox Tweaker?

Firefox Tweaker is a tool that allows users to easily control aka “tweak” hidden Firefox settings. These tweaks are mostly a result of silly design decisions by Mozilla and they go out of their way to make them super difficult to revert or change. Especially now that they have dumbed down about:config tweaks page even further…

How Firefox Tweaker applies tweaks?

This tweaker directly modifies settings within prefs.js file. Because Mozilla’s dumb idea is to kill user.js tweaks soon to save 0.000002 milliseconds of browser startup time, so I’m not even going to bother doing it through user.js and instead modify prefs.js directly. As a safety measure, backup of prefs.js is created on initial run of Firefox Tweaker. You will be notified about it on run-time.

Special thanks

I’d like to specially thank Mozilla designers/developers to bless us with moronic design decisions which forced me to develop this tool in order to easily revert or change them. I wouldn’t have to do it without you!

Warning and limitations

Because of bunch of dumb changes up till Firefox 77 and thus Firefox Tweaker 2.4, there will be some remaining tweaks left inside Firefox config from past changes. I’ve decided not to fiddle with them and try reverting them as it complicates things beyond what they already are and they are harmless and don’t really affect performance. With Firefox 78 we finally got another parameter that allows disabling of idiotic new oversized URL bar without having to use CSS, so there’s that.

Firefox Tweaker only works with Windows (and thus only supports Firefox for Windows).

Questions, problems or bugs?

For any questions, problems or bug reports contact me via e-mail or through comment section below.


Firefox Tweaker download


2.7.5 (2020-08-30)

  • Added “One Click Configuration” that will apply a curated selection of tweaks in one click.
  • Added “Restore Default Settings” option that can revert ALL Firefox Tweaker tweaks back to default settings in one click.

2.7.1 (2020-08-16)

  • Added option to Disable URL trimming (Interface Tweaks). URL trimming hides away “unimportant” parts of URL address to make it look easier to understand, but will hide URL specifics that might be useful to some. Disabling URL trimming should force Firefox to display full URL addresses at all times.

2.7 (2020-08-02)

  • Further enhanced disabling of WebRTC by enforcing (re-apply the tweak to enforce it)
  • Added new Disk Cache Capacity tweak for adjusting the disk caching between Automatic, Disabled, 1GB, 2GB, 3GB and 4GB capacities.
  • Added WebGPU tweak (Rendering Engine Tweaks)
  • Added Shaders Pre-Caching tweak (Rendering Engine Tweaks)
  • Added Force Sub-pixel AA tweak (Rendering Engine Tweaks)
  • Added Tiles tweak (Rendering Engine Tweaks)
  • Added warning for HTTP/3 as it is causing stalling/hanging of some webpages
  • Some updates of Help sections
  • Minor cleanup of code

2.6.1 (2020-07-26)

  • Added “Close tabs by double clicking” (Interface Tweaks). You can close focused tab by double clicking it. Might be more convenient than chasing a tiny close button on each tab.
  • Renamed few tweaks a bit so their names are not cut in the interface

2.6 (2020-07-13)

  • Added new “Rendering Engine Tweaks” category
  • Moved all the WebRender and rendering related features to new “Rendering Engine Tweaks” category
  • Added “Enable TCP FastOpen” tweak (Performance Tweaks) which should speed up successive TCP connection handshakes.
  • Added “Tracking Protection Performance Mode” (Performance Tweaks) which will apply lower network priority on content coming from tracking channels, giving higher priority to content you want to see and use.
  • Few minor fixes in Help descriptions

2.5 (2020-07-12)

  • Added new “Security Tweaks” category
  • Moved “Upgrade HTTP content on HTTPS pages” to new Security Tweaks category
  • Added “HTTPS Only Mode” (Security Tweaks) which strictly enforces use of HTTPS and blocks HTTP only webpages (Firefox 78+).
  • Few minor fixes in Help descriptions

2.4.4 (2020-07-09)

  • Fixed “Disable URL bar dropdown menu on focus” setting which now apparently uses “browser.urlbar.suggest.topsites” parameter instead of old “browser.urlbar.openViewOnFocus”. This change apparently happened with Firefox 78. While there is a setting in Firefox settings for this, I’m going to leave it in Firefox Tweaker for convenience reasons.

2.4.3 (2020-07-06)

  • Added “Enable HTTP/3” (Performance Tweaks). HTTP/3 uses QUIC mechanism to speed up connection negotiation and connecting to servers. Unsure when Firefox added support exactly, but it’s there for sure in Firefox 78 and newer.

2.4.2 (2020-06-30)

  • Upated “Disable new oversized URL bar” which now uses “ui.prefersReducedMotion” parameter to turn the damn thing off. Only works with Firefox 78 and hopefully in future versions too…

2.4 (2020-06-05)

  • Redesigned “Disable new oversized URL bar” which now uses userChrome.css style sheet in order to disable the god awful oversized dumbass new URL bar. Thank you for providing one.
  • Added mechanism to backup existing userChrome.css . It will still overwrite it entirely anyway when doing tweaks, but it’s there so you won’t lose all your own tweaks. Sorry, but this is the most I can do. Say thanks to Mozilla which forced me to do this god damn hack to disable their new URL bar.

2.3 (2020-06-01)

  • Added “Force Enable Direct2D” (Performance Tweaks)
  • Added “Force Enable HW Video Decoding” (Performance Tweaks)
  • Changed description in Help for “Disable new oversized URL bar” because dumb Mozilla decided to remove this tweak and shove this stupid new URL bar down everyone’s throats even though no one fucking likes it or ever asked for it. Disabling this oversized flashing ugly URL bar introduced with Firefox 75 is now only possible in Firefox 75 and 76. With Firefox 77 you have to use it whether you like it or not. You probably don’t. Enabling this with Firefox 77 will do nothing.

2.2 (2020-05-21)

  • Totally redesigned the prefs.js auto detection mechanism and added GUI driven manual selection or override for situations where prefs.js cannot be detected in default location or when multiple profiles are detected.
  • Added name of the exact parameter used for any given tweak under HELP button. Helpful so you know what exactly is being modified and if I’m interpreting some tweak wrong.
  • Added “Enable HTTPS green padlock” (Interface Tweaks)
  • Added “Disable Beacon API” (Privacy Tweaks)
  • Added “Browser Components” category
  • Added “Disable Firefox Accounts” (Browser Components)
  • Added “Disable Pocket” (Browser Components)
  • Added “Disable Screenshots Tool” (Browser Components)

2.1 (2020-05-09)

  • Added “Performance Tweaks” section
  • Added Enable WebRender setting
  • Added Force Enable WebRender setting
  • Added Force Enable Accelerated Layers setting
  • Added Enable GPU Process setting

2.0.1 (2020-04-29)

  • Added manual profile path override if default mechanism fails to find prefs.js file because your user profile is in non default location or you’re using portable Firefox. It can be done by placing PREFSJS.txt file next to Firefox Tweaker EXE and providing full path including filename and extension to desired prefs.js file inside this text file. There is now also actual file check in place which verifies if path provided is valid and points to actual physical file. If not, you will get an error letting you know you’ve set something wrong.

2.0 (2020-04-12)

  • New interface with modular design ready for the future
  • New custom designed Firefox Tweaker icon (Fox hugging a cog/gear)
  • Toned down the Mozilla hating wording
  • Descriptions of all tweaks are now inside the tweaker under Help button on every tweaks settings page
  • Added special setting to disable startup warning
  • Added quick shortcut to open Firefox Profile folder
  • Added function to clear “Your browser is being managed by your organization.” message
  • Added option to enable Container Tabs without having to install any extension
  • Added option to enable First Party Isolation
  • Added option to disable WebRTC functionality
  • Added option to allow 3rd party cookies for current session only
  • Added option for Firefox to automatically upgrade HTTP content on HTTPS pages to HTTPS as well if possible
  • Added option to disable Default Browser Agent telemetry function

1.0.1 (2020-04-10)

  • Forgot to enable Firefox detection mechanism and turn off some production debugging dialogs (you have only seen them if you had no Firefox installed when running Firefox Tweaker v1.0)

1.0 Initial release (2020-04-10)

  • Added “Disable browser closing on last tab close” (of all browsers only Opera isn’t doing this idiocy by default)
  • Added “Disable new oversized URL bar” (introduced with Firefox 75)
  • Added “Disable URL bar dropdwon menu on focus” (introduced with Firefox 75)
  • Added “Disable Add-ons recommendation”
  • Added “Disable Recent Highlights”

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