Google Chrome *might* have been a better bet than Chromium/Opera
Get Chrome from here:
(get the .deb version .. then just double click it to install)
Also it might have been worth COMPLETELY setting Firefox back to defaults by closing it, then whilst firefox is closed renaming the ~/.mozilla folder
then firing up Firefox again.
mv -v ~/.mozilla ~/.mozilla-original
The config directory will automatically get recreated on first run .. but you can always go back to the original by running the following 2 commands with Firefox closed:
mv -v ~/.mozilla-original ~/.mozilla
At the very least that would rule out a firefox config/cache/addon issue.