After updating to Firefox 92 I was greeted with a blank screen. A console had a "Quota Exceeded" DOM Exception logged.
I had to manually go to Page Info (Ctrl+I) and remove all data (browser reported 2Gb of data stored.
After clearing all data and using a QR code to log in the functionality has been regained.
Potentially the app should display instructions on how to mitigate the error.
Telegram Web 1.12.2 Z, Firefox 92