Hi. I faced the same kind of problem yesterday: I cannot login to the webmail on the version of Firefox installed through the package manager of my Ubuntu. However, using a Firefox downloaded from mozilla.org, I can login without problem. Here are the two versions of Firefox I am talking about:
* 129.0.1 (64 bits) - Mozilla snap for Ubuntu canonical-002 - 1.0 (Ubuntu package);
* 129.0.2 (64 bits) (Dowloaded from mozilla.org).
Today, the version of Firefox installed as an Ubuntu package updated to version 129.0.2 (64 bits) and I can login to the webmail.