Hi P4! Thank you for reporting, it looks like there are some website compatibility issues with Quora and the add-on, we'll add this to our backlog. For now, what I might recommend as a work around is go to the relay website: relay.firefox.com and create an email alias there, then use the quick copy button and you can paste an email alias into Quora's email address field. I just tested it out myself for you and it seems to work. Thanks for letting us know!

Updated: I just received a note from Quora that my Firefox Relay email alias was blocked. We'll try to reach out and see if we can work together.

Second Update: We received a great note from Quora and they're allowing the mozmail.com email domains now. Please let us know if you have any issues now P4.