I managed to do it with this:

@-moz-document url("chrome://browser/content/preferences/dialogs/translations.xhtml"){
 #alwaysTranslateLanguagesTree > treecols:nth-child(1) > treecol:nth-child(1) {
  color: red !important;
 }
}

in userContent outside of @-moz-document url("about:preferences")

But it doesn’t work in user chrome, it works in userContent but only if I don’t put it inside @ moz something. I don’t know why, I even created a new css file to do it and nothing.

@MrOtherGuy any ideas on what to do?

It doesn’t work.

But isn’t this code in userContent because about:preferences is a webpage?

Well I managed to make it movable with this: https://github.com/benzBrake/FirefoxCustomize/blob/master/userChromeJS/movablePanelUIButton.uc.js

So I don’t need help anymore :D

Thanks anyway!

I’m using a custom css and it changes the urlbar, Is it possible to put the hamburger menu where the downloads and extension are?

I’ll check it out, thanks!