Yes - see https://www.reddit.com/r/firefox/comments/bkcjoa/all_of_my_a... and https://www.reddit.com/r/firefox/comments/bk54mu/addonsexten...
Cannot tell if it's related to https://www.reddit.com/r/firefox/comments/bjwz8n/addon_polic... (Says new Add-On Policy effective June 10th, 2019, so shouldn't be causing this. But...)
As mentioned elsewhere, seems like when your clock hits 5/4 midnight UTC, you're done. I tried setting my clock in the past, but that did not fix the issue for me. (Clock was previously auto w/ daylight savings time enabled.)
Super interesting to watch /r/firefox go from 3.8k active/online users to 5.6k over the past half hour...
Edit: As mentioned below, there are GitHub/Bugzilla entries. They seem to be aware and starting to work towards a fix, though the explanation of the problem hasn't emerged yet.