To edit your your userContent.css file:

   First you need to find your Firefox profile. ...
   Under “Application Basics”, ...
   Look for the chrome folder inside your profile folder. ...
   Look for a file called userContent.css in the 'chrome' folder. ...
   Add the CSS and wrap-around text shown below.
   Save the file.
   Restart Firefox.

Try to make the code work for all namespaces. You can also try to place the code above the default @namespace line.

*|*tooltip {
 -moz-appearance: none !important;
 background-color: #1e1e1e !important;
 color: #b4b4b4 !important;
}

cor-el said

Try to make the code work for all namespaces. You can also try to place the code above the default @namespace line.

---

*|*tooltip {
 -moz-appearance: none !important;
 background-color: #1e1e1e !important;
 color: #b4b4b4 !important;
}

I tried your ways, but they didn't work for me.

Did you try to place the *|*tooltip {} code above the @namespace line because your screenshot shows your not working code in that position?

Tooltips are always difficult to get a selector or find them in the DOM and some elements in the user interface have been moved from XUL space to HTML space making this more difficult.

cor-el said

Did you try to place the *|*tooltip {} code above the @namespace line because your screenshot shows your not working code in that position? Tooltips are always difficult to get a selector or find them in the DOM and some elements in the user interface have been moved from XUL space to HTML space making this more difficult.

Thanks for your reply, but it didn't work either. Maybe it's a bug