Some over time have developed quite the collection of these files, taking up GB's of space. Firefox did this too on mine, taking room for cumulative Crash Reports over time, which I disabled to avoid it anymore.

Happens in Tor Browser too.

https://trac.torproject.org/projects/tor/ticket/9701

http://forums.fedoraforum.org/showthread.php?t=214318

https://bugzilla.mozilla.org/show_bug.cgi?id=335545

Fixed in 2010? Nope.

Just remember to find and check /tmp or /temp folders from time to time, not just for abandoned clipboardcache files, but other files abandoned there too.