Boris,

Firefox ESR 52.9.0 works fine.

Its a bit of a blabbermouth though (calls home to multiple servers, for
"location services" and the like). If you want to reign it in you'll need
to do quite a bit of about:config editing (apart from the ones that you can
access by the menu I mean) .

Of course, I have to make some boot floppies (chucked all of
mine years ago, damn), and see if they will be recognized by
an external USB floppy drive.

USB thumbdrives will mostly do as well.

As for the disk images themselves ? You can find a few here :
https://www.bootdisk.com/bootdisk.htm

Regards,
Rudy Wieser