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.
Although I sometimes have problems with Cloudflare, it does not seem to affect GitHub nor Gitlab for me, although they have other problems, which I have been able to work around.
Some things that I had found helpful when working with Gitlab is to add ".patch" on the end of commit URLs, and changing "blob" to "raw" in file URLs. (This works on GitHub as well.) It is also possible to use API, and sometimes the data can be found within the HTML the server sends to you without needing any additional requests (this seems to work on GitHub more reliably than on Gitlab though).
You could also clone the repository into your own computer in order to see the files (and then use the git command line to send any changes you make to the server), but that does not include issue tracker etc, and you might not want all of the files anyways, if the repository has a lot of files.
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.