In Firefox 91+ you can no longer disable Proton and revert changes that come with this design via "browser.proton.enabled = false" and other proton prefs on the about:config page. Best in Firefox 91+ is to set browser.proton.enabled at its default value true as the false setting can cause issues.

In Firefox 91+ you need to use code in userChrome.css to override changes coming with the Proton design.

• https://www.userchrome.org/what-is-userchrome-css.html
• https://www.userchrome.org/firefox-89-styling-proton-ui.html

Thank you cor-el I had already found this modification using css and do not believe I want to get involved with it I have happily used Firefox as my main Browser for over 10 years this upgrade has forced me to look for alternatives which can give me the look and feel of the Classic Interface Firefox more readily. I am finding more and more that developers are taking a course away from what users (specifically me) want and then locking the path so that you cannot easily get back the interface you have spent years tweaking to exactly what you want. Progress negative Usability zero

Goodbye Firefox Old Friend

Seconding this. I'm really disappointed that you have removed the option to disable Proton. UserChrome.css is not the most user friendly option and it's annoying to have to set up on each device.

Finding a tab is so difficult in Proton. Just run a simple experiment with 15+ tabs open and see how long it takes to find a specific one. My eyes are going crossed going back and forth to find a tab without any clear boundaries. The Container indicator is so thin that it's easily missed.

I would hate to do this but this may force me to move to Chrome and use their build in tab management as it has started affecting my productivity and seriously frustrating me. Take a look at the contrast this provides versus your design.

Chrome does look OK but I am not keen on using Google Products usually they come back to bite, Pale Moon looks OK under Win10 but not so much in Ubuntu Linux. Will keep looking Phil

Wow. I have a bookmarks folder on my toolbar that prior to these 'Proton' updates, would easily all fit on my monitor when I expanded the folder. With the new spacing from a Proton update, it was then cut off at the bottom and I'd have to scroll down to see bookmarks.

I posted about this issue and someone replied that I could change browser.proton.contextmenus.enabled to false, which fixed the issue. The issue is back again with the 91 update and this fix no longer works.

Now I have to start editing CSS to get the spacing reverted back? And what, move this local file across every device that I use Firefox on because it won't automatically sync? It's so incredibly frustrating when a company forcibly implements these types of changes that nobody is requesting.

I just reverted to FireFox 90.0b9 which appears to be the most recent version prior to 91. Add a Settings option for this, Mozilla!

Actually 90.0.2 seems to be the most recent version before 91, so I installed that one. Spacing fixed again. Won't be updating until this is sorted.

Do not think reverting is the answer, this means turning off automatic updates and the exposure to security vulnerabilties. Given the lack of response from Mozilla officialdom suspect this is not going to get sorted and will just have to move on. Are we in a minority us users of multiple Tabs and Long Lists of Bookmarks

Do not think reverting is the answer, this means turning off automatic updates and the exposure to security vulnerabilties. Given the lack of response from Mozilla officialdom suspect this is not going to get sorted and will just have to move on. Are we in a minority us users of multiple Tabs and Long Lists of Bookmarks

It's certainly not ideal but I utilize bookmarks regularly and so it's very impactful for me. This will have to be the solution until either Mozilla reverts the changes, adds a Setting, or I find another browser.