13 year old KDE bug fixed

Friendly reminder: it's been more than 15 years now, but we basically still can't have firefox handling textboxes right when using a dark gtk theme.

Link: https://bugzilla.mozilla.org/show_bug.cgi?id=70315

Previous submission: https://news.ycombinator.com/item?id=11147547

Wow, this affected me at Uni!