They do not support major browsers. They support "major browsers in default configuration without any extensions" (which is of course ridiculous proposition), forcing people to either abandon any privacy/security preserving measures they use, or to abandon the websites covered by CF.

I use uptodate Firefox, and was blocked from using company gitlab for months on end simply because I disabled some useless new web API in about:config way before CF started silently requiring it without any feature testing or meningful error message for the user. Just a redirect loop. Gitlab support forum was completely useless for this, just blaming the user.

So we dropped gitlab at the company and went with basic git over https hosting + cgit, rather than pay some company that will happily block us via some user hostile intermediary without any resolution. I figured out what was "wrong" (lack of feature testing for web API features CF uses, and lack of meaningful error message feedback to the user) after the move.