My machine runs current Win 10. Since the upgrade to Firefox 94.0.1 (64 bt) all hyperlinks from Thunderbird and Mailbird fail to open (no action occurs on click). If I change my default browser to Chrome or Edge the problem vanishes. Mailbird support suggested that I make sure that the protocol associations of ftp, http, and https are all set to the default browser--but Firefox does not appear as an association option for ftp.