Comment 8 for bug 111299

This is likely caused by https://bugzilla.mozilla.org/show_bug.cgi?id=296818 . To quote: "The thing is, the x11 pixmap is the _only_ place we're storing
our image data.". Apparently, there are many circumstances where Firefox does not request for that to be freed. (Ie. when crashing, but also potentially in other circumstances as well.)

I can definitely confirm this having existed since Firefox 0.3, on multiple distributions, multiple X versions (Xfree86/Xorg, along the years), multiple arches, and also on FreeBSD. I have restarted my X in average once per day because of this bug during these years.