Comment 35 for bug 20765

> Things that help: restart firefox (problem often reappears quickly though)
> Suspected dupes of this bug: 248345 (has some good comments), 266627

bug 248345 no longer applies as it has been duped to "large history file".
did you have another bug in mind? (perhaps you meant something other than bug 266627 cited above, which is this bug :)

you state restarting FF helps - does "clear private data" also help?

perhaps time to try the newest nightly build. And, without a clear cause or pointer to the cause and no objective data in the form of a debug or protocol log, you need to either eliminate more possibilities and/or go in search of other similar bugs.

So, changing component to tabbed browsing and suggest you attached an http log* and document a test case with steps and URLs.
* http://www.mozilla.org/projects/netlib/http/http-debugging.html