It's clunky, but I can open files in firefox by using a file browser app (I use x-plore), selecting 'open with', then selecting firefox. Sometimes it's not in the list, but there's a selector for what type of file (text, video, audio, '*'). '*' lists all the apps.
Sometimes stuff still refuses to open, but things like pdfs and html files usually work
Well there you go, Trump himself told us what happened. We can all go home.