Customize the maximum width of the Firefox sidebar?

Question

I have Firefox Quantum web-browser version 57.0.2 (64-bit) in Windows 7.

The Sidebar, unfortunately, has a maximum width of about 540 pixels.

I tried to increase this constraint by going to about:config and searching for "sidebar". Then I changed the setting devtools.toolbox.sidebar.width;500 to a value of 600. Then I restarted Firefox. But it did not work.

So how can I increase the maximum width of the sidebar?

Solution

1. Firefox menu -> Help -> Troubleshooting Information -> Profile folder -> Open folder

2. There should be folder named chrome (all lowercased). If it's missing, create it.

3. In said chrome folder, there's userChrome.css file. If it does not exist, create it.

4. Open this file with any text editor.

5. In this file, if there is no CSS rule #sidebar, create it:

/* remove maximum/minimum width restriction of sidebar */
#sidebar {
  max-width: none !important;
  min-width: 0px !important;
}

6. Restart Firefox

Comments

[u2n]

Confirmed in FF 66: No config settings work, but this method does. No way to improve it.

[wha7ever]

Did not work on FF 70.0.1.

[mini]

Since version 69 and later, Firefox does not load userChrome.css by default. To make it effective again, open about:config in Firefox and set the preference toolkit.legacyUserProfileCustomizations.stylesheets to true

[Marcin Orlowski]

Does not seem to work on FF 71.

[55 Cancri]

How do you guys know all of this stuff wth?

[ofer.sheffer]

Works in FF84(64bit) together with mini's suggestion above for changing the about:config toolkit to 'true' (default was 'false')

[ofer.sheffer]

Works in FF95.0.2(64bit) together with mini's suggestion above for changing the about:config toolkit to 'true' (default was 'false')

[Adám]

@ofer.sheffer (96.0) tookit didn't exist so I created it as Boolean and set it to True. I don't understand mini's suggestion, as I have no toolkit.legacyUserProfileCustomizations and can't see a way to create it so it can contain a stylesheets — I can only make it a simple value. An ideas?