Find a website that does not work in one browser, but works in another?
So a periodical reminder that such bugs can be reported via the #webcompat project: https://webcompat.com/
This often e.g. applies to sites, which are said to be incompatible in #Firefox or so, even though they work fine if you spoof your user agent.
Also if you use #Firefox you can type about:compat into your URL bar to see what workarounds (like spoofing the user agent) are currently employed to make websites work…