TYPO3 Core

Typo3 4.2.8, htmlArea RTE 1.7.11, in Firefox 3.5.2:
When I try to mark Text in the Editor with background-color, that has no effect. No change happens, neither in Backend, nor in frontend.

Astonishingly the feature works when I use an Firefox 3.0.11 or 3.0.13 Browser, but have to switch from wysiwyg-mode to text-mode and back before I can use it. If I fail to switch to text-mode and back, there is no effect on using the background-color button.
Unfortunately the trick with the switch in text-mode doesn´t work in Firefox 3.5.2

I tried the standard configurations of the htmlarea RTE Manual, none of them solved the problem.

The feature works in
- Opera 9.64
- Safari 4.0.3
- Firefox 3.0.11 and 3.0.13, but only when you changed from wysiwyg-mode to text-mode and back.
- Internet-Explorer 7 only when there are no <p> tags around the text (I don´t really care about IE, this browser is sometimes just annoying - so I list it only for the sake of completeness)

(issue imported from #M11857)