Google slides didn't work properly for me on Firefox a few days ago, all fonts displayed as some ugly serif font. Though I assume this is Google being underhand and malicious rather than Firefox not working properly.
Google is especially malicious, as they disable the mouse based past options in docs on firefox. This is a pain for users that don't know the paste shortcuts, or who are more comfortable with just using the menus. Sadly, the "dontfuckwithpaste" extension doesn't seem to fix it.