Thunderbird and Firefox fonts messed up in Gnome after installing and using KDE4 once

"kubuntu-desktop" is the package I installed, but I'm not 100% sure it is the right package to report against.

When using Firefox or Thunderbird in Gnome's Unity desktop after having used KDE4 once, the fonts in (at least) these two applications are messed up and cannot be restored with Gnome configuration tools (including MyUnity, "extended settings" and the like). See attached screenshots.

I tried removing Firefox's profile (~/.mozilla) which didn't help. I removed ~/.kde, ~/.kderc, ~/.gtkrc-2.0-kde4, .compiz, .dconf, .gnome2*, and almost everything else, and it didn't help. Only after removing *all* hidden directories and files - and thus restoring Gnome font settings to the defaults too - did Thunderbird and Firefox regain the ability to correctly display the fonts in use.

Note that the actual font which Firefox used for its UI *did* change when I changed the font in the Gnome settings tool. Only it looked totally ugly (without hinting?).

I would expect KDE4 not to touch Gnome settings while it is not running as a desktop environment - and vice versa. At the very least I would expect KDE4 not to change settings which cannot be restored with built-in configuration tools of the respective other desktop environment.