i think the summary tells it all.
Steps to Reproduce:
1. open a relatively big file containing lots of text f.ex.
2. go to "edit" "Find in this page..."
3. enter a search term, such as "13-rc"
4. hit "find" and then "cancel"
5. hold down Control-G untill...
multiple query boxes appears. they are empty (no text) but has 2 buttons (also
no text on them)
and none of the boxes can be closed, and thus the browser locks.
open one query box
Mozilla is dead upstream and will be removed from portage.