I went to sync my Firefox data on Endeavour OS, but my tablet died a couple weeks back and it had the authenticator app I used to generate the 2fa code needed. I dug out the list of recovery codes, entered one and got back to my Firefox account. In Firefox account I see that if you wish to change authentication it is necessary to delete the old one and create a new one. That proved to be a headache. The camera on my phone failed to read the QR code generated and my thumb is a bit over half the size of the phone keyboard, so I had zero luck entering the 25 character alphanumeric string instead. So in the end I just had to disable 2fa.
I believe that 2fa is good and secure and I try to use it, but the tech places that want it used really need to figure out an easily human way of doing it. I have a Yubi, which works very well on the three places that actually use it. Windows and Mac have face id and touch id which seems easy and efficient for 2fa things. I can buy stuff by tapping my card or phone on a reader, my car unlocks when I walk up to it. It really seems that syncing bookmarks and tabs on Firefox could be easier.