Disable Proton in Firefox 91

If you don't like the new look of the browser, we will show you how to disable Proton in Firefox 91. Earlier, you could disable it with a couple of settings in about:config. Now, you should use a different method.


Actual versions of Firefox include a new user interface, known as Proton. It is notable for rounder corners, less contrast colors, and other similar changes that make the browser go well with the style of the newest Windows 11. Also, the changes made it more touch friendly.

However, many users didn't welcome the updates to the browser's look. The poor contrast of controls makes it harder to spot elements. Tabs look like buttons and feel completely disconnected from the tab row. There are no separation lines clearly defining tabs which makes multiple tabs look like one connected button. Finally, the huge control spacing looks weird on regular desktop PCs. Also, menus without icons and feel lost and empty.

How to Disable Proton UI in Firefox 91

To disable Proton after updating to Firefox 91,  you need to do the following.

  • Enable support for userChrome.css
  • Apply CSS styles to disable Proton tabs and buttons.

Firefox 91 Disable Proton

Here are details on each and every step.

Enable support for userChrome.css

By default, Firefox doesn't process userChrome.css or userContent.css files which store user-made customizations for the user interface of the browser. You need to enable them We have a dedicated tutorial on this topic here on Winaero. Here are the steps you need to perform.

  1. Open Firefox and type about:config in the address bar. Press Enter.
  2. Confirm that you accept the risk.Firefox About Config
  3. Paste toolkit.legacyUserProfileCustomizations.stylesheets into the search box.
  4. Set the toolkit.legacyUserProfileCustomizations.stylesheets value to true.Firefox Enable UserChrome Css
  5. Restart the Firefox browser.

Done. This will enable support for CSS customizations in Firefox 91. You can now disable Proton. Here is how.

Disable Proton in Firefox 91 user interface

There is a project on GitHub that maintains the custom style to revert Proton in Firefox and restore its previous look.

To disable Proton in Firefox 91, do the following.

  1. Click on this link to download the ZIP archive with CSS styles.
  2. After that, type about:support in the Firefox address bar.
  3. Click on the Open Directory button next to the Profile Directory entry. This will open your Firefox profile folder in File Explorer.Firefox Open Profile Folder
  4. Extract the Firefox-UI-Fix-photon-style folder from the ZIP archive you have downloaded to that folder.Copy Styles To Profile Dir
  5. Rename the your firefox profile dir\Firefox-UI-Fix-photon-style folder to chrome.Firefox Rename Folder To Chrome To Disable Proton
  6. Now, open the chrome folder, and cut (Ctrl + X) the user.js from there.Cut User Js File
  7. Go one level up, i.e. to your Firefox profile dir, and paste the user.js file (Ctrl + V).Disable Proton Paste User Js To Firefox Profile
  8. Return to the Firefox about:support page and click on the Clear startup cache... button at the top.Restart Firefox Clear Cache
  9. This will restart the browser. Enjoy the now-classic "Photon" look of Firefox 60x.Firefox Restart To Disable Proton

That's how you disable Proton in Firefox 91.

Don't turn off other parameters in about:config

While Firefox 91 retains all the *proton* options in about:config. But you should not disable any of them. Please keep them to their default values. Otherwise the customizations you made won't work properly.

They are required to "restyle" the browser's appearance and disable the Proton UI.

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21 thoughts on “Disable Proton in Firefox 91

  1. Hartwig Kipp

    Hello Mr. Tkachenko,
    many thanks for the good working, well described and illustrated tutorial!

    1. Sergey Tkachenko Post author

      you are most welcome sir

  2. Peter

    Thank you!

    1. Sergey Tkachenko Post author

      you are welcome

  3. Ivan Burmistrov

    Tabs improved, but toolbar is still low-contrast and there is no circle around “back” button.

    1. Charky

      Good, I hate the circle around the back button.

  4. Gustavo

    You saved me! Thanks!

  5. Charky

    Thank you for this tutorial! Hoping Mozilla realizes that Proton sucks.

    1. Sergey Tkachenko Post author

      It looks like they like the changes.

  6. Mario Rossi

    Thank you very much! I hate proton!!!

  7. Rudie

    Great thanks! — real tabs! compact menus!
    Only thing is the horrible rounded corners on the menus remain.

  8. bblackmoor

    This worked! Thank you so much.

    1. Sergey Tkachenko Post author

      You are most welcome

  9. Anne

    It didn’t work for me. :( I don’t know what I did wrong but I’m looking for a new browser I guess because the tab bar really bothers my eyes.

  10. Mark

    Perfect! Thank you!

  11. Pam

    Holy thank you, I wish Firefox would just let us turn the theme off if we don’t like it!

  12. Mike Oxmaul

    Thank you so much <3

  13. Tsami

    FF 91 & 92 removes the color from the tab bar whether or not the window is active, and this restores that feature. So, thanks very much for that.

    I applied the two .css files separately, already having a chrome folder containing .css files from before. After adding the contents of the new userChrome.css file to the old one, Proton was gone and everything worked OK. Adding the new userContent.css file didn’t seem to change anything. Will something bad happen if I just continue using the old userContent.css file?

  14. Tom

    What utter *ssholes! I have to go through ALL OF THIS COMPLETE BS just to get proper spacing for my bookmark dropdowns?!?? I guess it’s time to look for a browser developed by intelligent human beings who respect their customers. GOOD FREAKING GRIEF, THIS IS TERRIBLE, HORRIBLE, MISERABLE.

  15. Paolo Del Re

    Thanks a lot Sergey, very good job to make it easy for everyone to restore the previous style without knowing how to work with userChrome and edit the CSS files.
    Without this, I would have switched to MS Edge already, after being faithful to FF for 15 years. Main reason is to regain the precious vertical space, that with MS Edge is very possible by enabling vertical tabs.

    Like someone else has already commented, would it be possible to improve the contrast between the address bar and the toolbar (just like it was until FF 88)? Currently, the box is greyish until you click on it to write something, then it turns white. The initial greyish color is just slightly darker than then gray toolbar color.
    Until FF 88 the address bar was always white (before AND after clicking on it) and the toolbar grey color was also a little darker.

    Thank you again for the great job!

  16. Jose_49

    Nice. Thanks a bunch. Although I’m not against Proton UI I wanted to keep the previous one because Proton’s look a lot like Edge and I was barely able to differentiate it


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