For years I've used the same email and password to login to Firefox sync. However I discovered in recent weeks my login details are no longer recognised., so am not able to import all my bookmarks and online passwords onto a re-installed operating system. My stored passwords on another system visibly shows the same login details I have always used. This has not happened before, and I did not change my login details, so I am at a loss what has gone wrong.

Any suggestions as to how I can login to syncing.