I use a 2021 Macbook Pro with all updated software. I consider Firefox my main web browser. I have a Weebly website that I can always log into with Safari. But with Firefox, every few months or so, I'll get a message that the email address I use to log on is incorrect. The message usually lasts 2-3 weeks or so, and then, it mysteriously goes away and I can log in again (for a while). It has happened four times. Right now I'm in week 3 of not being able to log on with Firefox. I have no idea if this is connected or not, but it all began shortly after I started using the Firefox Delay extension. I don't use it any more and the problem still happens, so it is a big question mark. I only used the delay extension to log onto two websites - my weebly site and also my Craigslist ads. I've only had problems with these two accounts since then. I opened new accounts on Craigslist after stopping the delay extension - but I still have trouble with Craigslist email. I get emails from customers answering my ads but when I reply, I get a message that it was undeliverable, even though I think my reply was in fact, delivered. In both cases, the problem is with my email.