> They should probably test their account creation form in every major browser, since different browsers use different algorithms for generating secure passwords.

Firefox has largely stopped being a major browser. It is battling Opera and Samsung Internet for 4th place. So even if they did test with major browsers, it may still not have worked.

Anecdotally within my network and at my own employers when I have been involved in the testing pipeline, Firefox has been decommissioned as soon as it started requiring unique fixes vs Chrome/Safari.