Just FYI: I tested the registration process in Firefox on two different systems (Win 7 and Win 10), but wasn't able to replicate any problem. I also briefly ran this past development. It's not clear what would have been the issue. Maybe a temporary one, or maybe a conflict with a specific Firefox browser plug-in. Either way, it doesn't seem to be a general problem, and you're hopefully not going to have any issues using the website with Firefox now.
There is a definite problem. Although I have got FireFox somehow to store the password, I still have to log in each and every time I visit. This started a few day ago. I can never get to the 'remember me' box that appears to tick it before it disappears after I've pressed the Blue Arrow.
There have been four updates to Firefox in the last few weeks. I have had no issue with Firefox remembering the login options, however I did had a different issue with Firefox 2 versions ago trying to upload and a layout issue, however these are now fixed currently on 67.0.2
I tried twice. The second time I copied and pasted text straight from a plain text document and then tried to insert images straight away thinking the same thing as you. It's didn't work. Only after pressing the edit button after posting was I able to upload my images.