If using version 55 as it shows here you are running a unsupported and insecure browser.

Current Release Firefox 57.0 with a Full Version Installer https://www.mozilla.org/firefox/all/ or 52.5.0 ESR is secure. It will continue to get security updates until May 2018, and you can download and install it from this page: https://www.mozilla.org/en-US/firefox/organizations/all/ Note : Legacy Extensions will be deleted or removed in any version update after May 2018.

You should make a backup of your Profile before going back and just because: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Please let us know if this solved your issue or if need further assistance.

Thanks, the longer I can avoid Quantum the better.

Ok, tried the ESR, it immediately disabled necessary extensions. Can you tell me how to revert to 55?

Never mind, thanks, figured it out.

The only question remains: how do I download things like Google Backup & Sync, when I click on buttons and they don't work?

I didn't seem to have had problems with that in the past with Firefox. So, is that permanently gone in 55, or is it only gone because Quantum came out?

I really DO NOT want to upgrade to Quantum. It crashes too many extensions. If I wanted FF to be Chrome, I'd just use Chrome. The extensions are far more important to me than gaining a 10th of a second here and there. I do not want the ESR release--it's old and it also crashed an extension.

So, are my choices now reduced to versions that crash my extensions or a version that won't download things like Google Backup & Sync?

None of those are good choices. Back to the original point, assuming the failure to download is a javascript issue, how do I enable javascript in FF 55?