I've recently seen quite a few reports of issues with accessing Google Calendar, so it looks that something is seriously wrong.
You can check the Web Console for possible error messages.
You can try to hide and show this content to see if that has effect.
There has been a bug report created where you can follow the progress.
- Bug 1688211 - Firefox sometimes failed to load Google Calendar
(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)
I've recently seen quite a few reports of issues with accessing Google Calendar, so it looks that something is seriously wrong.
You can check the Web Console for possible error messages.
*https://developer.mozilla.org/en-US/docs/Tools/Web_Console
You can try to hide and show this content to see if that has effect.
There has been a bug report created where you can follow the progress.
*[https://bugzilla.mozilla.org/show_bug.cgi?id=1688211 Bug 1688211] - Firefox sometimes failed to load Google Calendar
(<i>please do not comment in bug reports<br>https://bugzilla.mozilla.org/page.cgi?id=etiquette.html</i>)