Ah now thats a whole 'nuther story. Can I ask from what old OS version to what new version? Although its different software I recently updated two Airport home wifi base stations to the latest firmware versions and found the updates completely stuffed my household wireless network: no internet, no printing, no backups. Had to uninstall the upgrades and reconfigure the whole feckin system….. no fun that job at all.

As far as standard Mac OS's I haven't gone beyond 10.7.5 despite all the so called improved user 'experience' as I don't want the expense of upgrading other key software that works perfectly fine as is. This works on that other classic piece of IT wisdom: "if it aint broke, don't fix it"! In your case as you say the Firefox options should work just fine. One thing though watch out as Firefox keeps being updated and the interface keeps changing all the time too.

Cheers,

Andrez