I seem to have the same problem with a friends computer using Mychart. Firefox does have the ability to generate a secure password if requested. I didn't request any such password. Entered a new password and told FF to save it when asked. Went to the site, signed off, and tried to login again. It failed. Went to pword manager to look at password and it wasn't there - just an alphabet soup. Happened again. I suspected Mychart but I'm not aware of how they can return a secure pword to firefox nor why they would want to.