Black on black tooltips in Firefox with Kubuntu

I use Firefox on Kubuntu, and for a long time I had an issue with the tooltips: the characters were printed in black on a black background (a slightly different shade of black, but still very difficult to read).

I used to have a solution with Stylish, but it broke in Firefox 57 (Firefox Quantum). Here is a solution which works now, for anyone else with the same issue.

  • Navigate to ~/.mozilla/firefox/
  • Find your Firefox profile: a folder with a name like 1rsnaite.default
  • Navigate to ~/.mozilla/firefox/1rsnaite.default/chrome/ or whatnot (you might need to create the chrome/ folder)
  • Using your favourite text editor, open the file ~/.mozilla/firefox/1rsnaite.default/chrome/userChrome.css (creating it if necessary)
  • In this file, put the following code:
  • /* AGENT_SHEET */
    @namespace xul url(;
     color:#FFFFFF !important;
  • Save and restart Firefox.
  • If you have several profiles, repeat for the other profiles.

I am not an expert at these things; if this does not work for you, I won’t be able to help you any better than Google.

I used the following sites to find this solution:

2 thoughts on “Black on black tooltips in Firefox with Kubuntu

  1. Thank you for your post! I just got the same problem in Kubuntu after upgrading my system, including firefox. I tried your solution (with bcolor: #FFFFFF – otherwise there wasn’t much contrast) but managed to make only some tooltips visible. After studying the issue I begun to suspect the problem was the oxygen theme for Gtk3. A simple solution was going to system settings -> Application appearance -> Gtk and selecting Default for the GTK3Theme. (I had only oxygen, Default and Emacs available and the latter two seemed to produce the same tooltips). Now all tooltips are visible although colours could be nicer. Any ideas how to modify these are welcome!

    1. Thanks! I updated my post to handle other kinds of tooltips, and with #FFFFFF to make them more visible.
      I agree the problem probably comes from the Gtk3 theme, but I never managed to get another theme to work better.
      For some reason, editing the background colour doesn’t work with my solution; I don’t understand where that colour is set.

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