Not saying I should have to accept that, but that's what it was.
Certainly not 'regularly'.
I also do really not experience it "regularly", but different people visit different sites.
That said, the one problem I get most often is this Cloudfare one.
There are several plugins for Firefox that make this easy.
Google drive is another one, where some things stop working depending on the user agent I'm presenting.
UA sniffing is soooo 2008.
It's absurd that this is even possible. They should at least provide troubleshooting advice for end users.
Looks like there are already a couple bug reports about whatsapp.com, but not the forever-refreshing page you see:
https://webcompat.com/issues?page=1&per_page=50&state=open&s...
Unused, mostly, but installed :)
Sadly I find it happens more and more often, even with important things like financial services.
What I haven't figured out yet is whether it's really the Firefox engine that is the problem or just that Firefox also provides better tools for blocking obnoxious trackers and the like. Maybe because I have those tools turned on by default more sites using obnoxious trackers break in Firefox than other browsers. In most cases that is a feature not a bug but it's frustrating when essential functionality on sites providing essential services gets broken as collateral damage.
On large international sites the likelihood that Firefox works flawlessly is pretty high. But a lot of regional service providers appear to kind of have given up on it.