Proton makes updates to their service time by time and every update breaks compatibility with a large old version browsers and systems. They do not consider that all hardware cannot work smoothly with latest OS versions and therefore, they have to use older browsers.

In addition, some browsers which have many advantages over other browsers regarding stability and performance -like seamonkey- are not supported by proton at all.

I know their reasoning is "update for security" but experience shows that servers who rely on day to day update are less secure because they do not informed well about security principals and expect updating or using latest versions of development tool kits keeps them secure.

Proton criticizes google and other high techs for their monopoly policies while they test primarily their products to work with google chrome and do not concern about alternatives. This behavior is observed on many web sites today. Once they see their website/server works on google chrome well, they say it is OK; not important has problem with other browsers or not.

I suggest please make a slim, pure html based version of proton to be compatible to all browsers though not supporting all features but at least the email service.