it's pretty rare to see non-Google sites which only work in Chrome.
Unfortunately that hasn't been my experience in recent months. A noticeable number of random sites I come across, sometimes including quite important ones, Just Don't Work in Firefox.
Is there a quick way to send a link to such sites/pages, if someone at Mozilla is interested in investigating why?
I think it's important to note that this behaviour isn't necessarily due to anything wrong with Firefox. It could simply be because Firefox is better at blocking unwanted content than certain other browsers and that feature is working as intended, but the kinds of sites that rely on hostile content also tend to break if those scripts are forcibly blocked by the browser.