Can anyone who is seeing this bug please do the following (WITH FIREFOX NOT RUNNING)

  mv ~/.mozilla ~/.mozilla.backup
  firefox "data:text/html,<script>window.close()</script>"
  cp ~/.mozilla.backup/firefox//urlclassifier* ~/.mozilla/firefox//
  tar -cjf mozilla-421482-profile.tar.bz2 ~/.mozilla

If firefox is still unusable after these steps, then please attach mozilla-421482-profile.tar.bz2 to https://bugzilla.redhat.com/show_bug.cgi?id=439908