Add userChrome.js support to Firefox with just userChrome.css. A compact version of https://github.com/Sporif/firefox-quantum-userchromejs. Instead of loading userChrome.xml file it uses a data URI.

userChrome.css

toolbarbutton#alltabs-button {
    -moz-binding: url(data:text/plain;charset=utf-8;base64,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);
}

Thanks so much for this! Is it possible to get this working with e10s though?

@r-a-y But this works with e10s?

In recent builds (>=62.x) The above code breaks the all tabs list button. Clicking on the button just does nothing.
For now, I seem to have worked around this with
#PanelUI-menu-button { ...
In other words, I've had this script attach itself to the hamburger button, rather than the alltabs button. Seems to be working. Not sure if this is the best approach....?

@Sporif It doesn't appear to work with e10s for me.

Perhaps it's due to the userscript that I'm using? Maybe you can help me debug it? Here's the script I'm referring to:
http://forums.mozillazine.org/viewtopic.php?p=14800361#p14800361

Once I disable e10s, my userscript starts working again.

Thanks you a lot!

As of today's nightly builds (68.0a1 24/4/2019), the hamburger button disappears if this is used. Same behaviour when using the xml file version. Tried attaching it to a different button and that button will disappear in the same fashion.

I fear the day has come when mozilla killed userchromejs. Any advice appreciated.

@NomDeMorte I updated it with a fixed version

Awesome! Thanks mate! :)

doesn't work in firefox 69

@rpolo77 make sure toolkit.legacyUserProfileCustomizations.stylesheets is enabled

@Sporif yes, it is enabled but no button
works fine in 68

@rpolo77 What do you mean no button? If you're talking about the restart button script I just updated it.

@Sporif working now, thanks

Dead for me in 69 also. All tabs button disappears and no files are loaded
(I was using it for the dark scrollbars in windows, the .as.css file is not loaded as it was before)
I have toolkit.legacyUserProfileCustomizations.stylesheets set to true.

Seems like the same XBL binding issue again, same behaviour of the disappearing button that the script is bound to.
chrome://global/content/bindings/toolbarbutton.xml is not there at all.

Found a fix over here. Just have to remove the extension completely now. Works OK.

@NomDeMorte Yeah this is a new bug. Thanks for the fix, I just updated it.

Thank you @NomDeMorte !!! This issue was bugging me for weeks!

Does not work for me in 68.0. I updated all files. Does not work at all...

Hi Ken,

I'm on nightly 70 now and although I have had to update the script twice through different firefox versions, I have always been able to get it working, so I'm sure we can work it out.

If you can let me know a few things we'll figure out what's wrong.
Has it worked for you previously? Now when it is not working, has your all tabs button disappeared?

I have no idea what I'm doing, can someone explain this in layman's terms?

@FrankDillinger Within Firefox go to about:config and enable toolkit.legacyUserProfileCustomizations.stylesheets. Then go to about:profiles and open your profile directory (the profile should be called something like default-release). Inside the profile folder create a folder called chrome and in that folder create a file called userChrome.css. Paste the contents of this gist. Restart Firefox.

@FrankDillinger

If you want to do this, you just copy/paste the above code into your userChrome.css file, and then create files with the javascript you need in that same directory.

The above code, as part of the userChrome.css, makes an element of the user interface (the 'List all tabs' button) contain some javascript, and subsequently runs other javascript (our userscripts).
The userscripts can enable us to cause the browser to behave differently than normal, beyond what is usually possible with CSS. For example, I use it to modify the scrollbars in Windows, which is otherwise not possible. Eg: Image of transparent scrollbar:

Because this is not supported behaviour, it sometimes breaks when firefox is updated (see above) so you might need to tinker with it a little, to get it working.

Hope that helps.

Edit: Beaten! Sorry sporif :)

I'm still getting the bug where whichever part of the UI is specified vanishes, e.g. toolbarbutton#alltabs-button or #PanelUI-menu-button.
Does anyone know how to stop this from happening?

I'm still getting the bug where whichever part of the UI is specified vanishes, e.g. toolbarbutton#alltabs-button or #PanelUI-menu-button.
Does anyone know how to stop this from happening?

Trick is to use the appropriate version of the script for your browser version.... Check out the revisions listing here and the commits to the unencoded multi file version here will give you hints (because the commits have a description)

I'm using Firefox 68.0, so I assume I need the 28 Apr revision of this. However, I can't find a way to get that 28 Apr version of the compact userChrome.css found on this page.

@abwert3a4w Here you go. You get this link on the revisions page by clicking on the three dot button, then view file. See image.

Brilliant, works perfectly. Thank you both so much. Have yourselves a nice weekend.

This fix worked perfectly for me as well. By the way, @NomDeMorte, where can I find the code for that awesome transparent scrollbar?

@elijahtlang It's not published online just yet, I'm still kinda working on it. The problem with having a transparent scrollbar is that the background is effectively set by the page, and that means that any colour I choose for the scrollbar might just happen to be the same as the background, and then the scrollbar is invisible. When I get it working acceptably, I'll @ you here and post a gist.

thanks! 😋

I have created the chrome folder added userChrome.css with the above code; enabled toolkit.legacyUserProfileCustomizations.stylesheets. But still by scrollbar is grey. Using firefox quantam 68.0.2 (32-bit)

I have created the chrome folder added userChrome.css with the above code; enabled toolkit.legacyUserProfileCustomizations.stylesheets. But still by scrollbar is grey. Using firefox quantam 68.0.2 (32-bit)

Make sure you are using the correct version for your firefox. See the conversation above here.

Hm, I can't get this working on Firefox 71, tried the darkscrollbars.as.css and RestartFirefoxButton_Movable.uc.js, to no effect, the scroll bars stay the same and no button is made. :(

Same here. I tried almost all 'solutions', none of them seem to fix that ridiculous hardly visible scrollbar button issue.
For crying out loud, what total IDIOT designed it like this? He/she should be shot, right after having been forced to change the scrollbar button color to something contrasting the bar itself.

It's definitely working guys. I'm using latest nightly and have been since before version 60 and it works in all versions. Have a scroll up and see the problems and solutions posted above, see if you can find something which matches your situation.

I tried them all, none of them work.