KB2670838 and the font rendering issue in Firefox

Three months after installing KB2670838 and updating my graphics drivers from Catalyst Mobility 13.12 to 14.4 the font rendering issue popped up. Except I didn’t get issues with text rendered in pages, but in Firefox’s menu /tabs / titlebar itself.

Nobody would think an update installed that long ago could be the culprit. Everyone would think the newly installed driver is (and it definitely has something do to with the issue).