Not sure it's related but a lot of Google's sites are terrible on Firefox and Edge. IIRC they are using polyfills for some heavy stuff (if you assume no malice, that's probably the cause of many problems).
Try using safe-mode https://support.mozilla.org/en-US/kb/troubleshoot-firefox-is... or maybe creating a new profile. The beta versions, just like Chromium or Chrome, occasionally have some weird bugs. At least for me most of them are always hardware acceleration related.
I've had trouble accessing the Google Analytics dashboard(s) in FF as well. Nothing gets rendered except the background gradient.
In the interest of not using Chrome though, when I run into such issues I use Brave as it's Chromium-based and thus allows me to side-step those problems.
The times I had problems with GA was because of some uBlock rule or weird A/B tests (I assume) or caching, clearing cookies and site data fixed the problem.
In the interest of not using Chrome though, when I run into such issues I use Brave as it's Chromium-based and thus allows me to side-step those problems.