Description of problem:
firefox freezes on some pages for about 1 or more minutes

Version-Release number of selected component (if applicable):
firefox-22.0-1.fc18.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Go to https://secure.avaaz.org and klick on the slideshow
2. or go to https://support.mozilla.org/en-US/kb/avoid-crashes-tips-and-tricks

Actual results:
Firefox freezes for 1 or more minutes (i did not stop the time, but it is more than one minute ...)
cpu usage is about zero (maybe a few procent, but not much)
Memory load stays constant

Expected results:
Stay responsive

Additional info:
Happend also with FF 21
Happens also with all plugins disabled or a new user.
Wirks fine with the binaries direct from mozilla.org

Most other pages work fine