For example, on https://drive.google.com/drive/home ?

Does it make any difference to:

• Reload the page bypassing the cache (Ctrl+Shift+R or Shift+click the Reload button on the toolbar)?
• Create an exception to Tracking Protection by clicking shield icon at the left end of the address bar (before the lock) and then clicking the slider switch to turn off TP on the site?

Related thread: https://support.mozilla.org/questions/1476200 (Drive works in private window but not regular windows)

Another user said it's caused by Adblocker Ultimate (here). See whether you can make an exception for Google sites.

I have had the exact same issue, and it resolved after I disabled AdBlocker Ultimate on Google Drive (thanks jscher2000 for letting me know, and saving my day)

Solved! It was the Ad blocker extension. Thank you all for your help!

I submitted a support request to the company and got this message back overnight:

From: Alex from AdBlocker Ultimate <support@adblockultimate.net> Hello Please update the adblock filters in the browser extension settings. The issue will be fixed.

So if you disabled it completely, you should now be able to use it again. Hopefully.