Screenshot at: http://mysterion.org/~danw/f11-redhat-bugzilla.png This was in a firefox that had been running for a while. When I quit and restarted, there were only one or two bad glyphs. The problem has shown up on other sites too, mostly with bold text.
Thanks for the bug report. We have reviewed the information you have provided above, and there is some additional information we require that will be helpful in our diagnosis of this issue. Please attach your X server config file (/etc/X11/xorg.conf, if available) and X server log file (/var/log/Xorg.*.log) to the bug report as individual uncompressed file attachments using the bugzilla file attachment link below. Could you please also try to run without any /etc/X11/xorg.conf (if you have one) whatsoever and let X11 autodetect your display and video card? Attach to this bug /var/log/Xorg.0.log from this attempt as well, please. We will review this issue again once you've had a chance to attach this information. Thanks in advance.
Created attachment 342317 [details] Xorg.0.log I have no Xorg.conf. (Also, FWIW, your stock text is wrong; it refers to "the bugzilla file attachment link below", but it's actually *above*. :)
This is a dupe of the intel driver bug -- new kernel dropped a libdrm patch here, and it hasn't been backported yet. You'll note that anything using fonts will eventually have this problem after enough uptime.
*** This bug has been marked as a duplicate of bug 495323 ***