When I try to sign into Firefox Sync after typing in my email for the account it just says "working" and the progress bar spins but the page never loads for me to put my password in. I let it sit there for almost a half hour and no progress. I am up to date and have tried restarting and shutting down the phone and Firefox.
@publiclewdness I think you might need to change the useragent to a different one, i remember someone having this issue. feel free to join our telegram or matrix group and ask questions, you will get better answers there.
release 13.0.7 will fix all of these issues soon. we used to use an android user agent to make websites show their adaptive and mobile friendly version but this made some websites unhappy. the new release will bring a webcompat-like solution which allows to set exceptions for useragent
I had the same difficulty on 4 days running. I went to the Firefox and tried to report the error on the site after posting a case on Bugzilla. I actually managed to reach a contact site for Firefox problems and had to log in there. Figuring that I was already logged on to the browser, I went back to the Sync application (not having left the other page) and was able to get the Sync running. Once any sync is performed, there is listed in the passwords of any device, here the Furi FLX-1 a password for accounts.firefox.com so that future Syncs should be accepted automatically. Hopefully this can be made to work for you as well.
I also ran into this signing into firefox sync. I ended up changing the useragent by going to about:config and searching for useragent to find general.useragent.override and set it to
Mozilla/5.0 (X11; Linux aarch64; Mobile; rv:133.0) Gecko/20100101 Firefox/133.0
which is why my pinephone used. This allowed me to sign in to firefox after reloading the sign in page. The original one didn't look like a firefox useragent so I'm guessing firefox thought I was trying to sign in on a non-firefox browser and got confused.