Firefox 社群討論區

I'm running Firefox browser 88.0 (64) bit, and have been trying since before Xmas to upgrade it to a newer version. It's installed on an older Dell laptop running Ubuntu 16.04 LTS (which I've also tried repeatedly to upgrade without success).

I've tried to upgrade both through the UI, but also tried using the command line in Terminal. Per advice in other threads, I've found the best mirror site and changed my settings to use that, but still no luck. Even the preliminary "sudo apt update" via Terminal fails; the first error tells me that the public key is not available. I assume that's the place to start, but don't know how to correct it.

I'm up against the deadline for updating my browser, and would very much appreciate any help you can provide. (Please note that I'm posting from a newer computer, so automatically generated info about my system won't apply. See the screenshots for that info).

Hi My version of Firefox will not be supported after Jan 14th - I can't download an updated version of Firefox because my Mac is IOS 10.10 and apparently it needs to be at least IOS 12. What can I do? I will be updating my computer but I don't want to lose access to my docs etc on the 14th Jan. Thank you - I would appreciate help please.