Maighstir: The file is the same you already used (you said what you did only removes the icons in the bookmark toolbar, so I just assumed you'd see that my code is similar and belongs in there as well). Just copy the code and paste my code in there. At least the second of those three bits. The last you already tried (and, as the comment says, is used for the bookmark toolbar).
EDIT: If you don't use userChrome.css for anything else, just remove the entire contents of that file, then copy the second and third of the three rules in my post and paste into that file, finally close the browser and start it up again.
joelandsonja: It doesn't work, but I'm not sure if everything has been pasted properly in the document (I will include a screenshot).
That is weird. Did you completely shut down and start up Firefox after the change?
The fact that there are two rules for "toolbarbutton-icon" shouldn't matter, they both say the same thing, and the former is the one that's used since it's more specific.
The one you pasted from an earlier instruction basically says:
Find the specific element with the ID "PlacesToolbarItems"
Find all children of said element with the class "bookmark-item"
Find all children of those with the class "toolbarbutton-icon", and make them hidden, regardless of other rules.
Mine instead says:
Find all elements with the class bookmark-item
Find all descendants of those, and make them hidden regardless of other rules.
You could try removing or commenting out the @namespace line, it's not necessary, and may even hurt (that is, it may make your rules
not apply).
To comment it out (meaning, Firefox will ignore it), follow the same pattern as the "human-readable" text already in the file - put
/* at the beginning (right before the @), and
*/ at the end (right after the ; in the first line).
