I have used Firefox for about a decade now and I can't think of a single page that did not work. I'm not saying it's impossible, but incredibly rare. I'd be more inclined to just give up on the site than install Chrome.
And I have had a few experiences with sites not loading properly in the last few months. Try windy.com for example: on FF 90 with no extensions enabled and tracking protection on 'balanced' I get blue and yellow banding on the map, and the wind gusts graphics fail to load properly. I have reported a few of these instances in the past, but a lot of the time I'd rather just switch to chromium temporarily and continue with what I'm doing.
[0] https://www.cnet.com/tech/services-and-software/mozilla-exec...
I do wonder if every user would be aware that the 'Allow site to extract canvas data?' popup can break site functionality though -- its not as though there's a warning to that effect in browser.
A hassle but well worth it to avoid touching Chrome ;-)
But it turns out the difference was the I was running ublock-origin in Firefox and sometimes that was causing issues for some sites..