Hm you're right. At some point I could no longer move lists around, but it's back now. It was the third UI to break after Intercom (customer replies not shown unless I reloaded) and Notion (down arrow does not scroll the page down), so I tried Chrome and it fixed the problem. Maybe I should have tried restarting Firefox...

Yes, I've found that now and then after a few weeks of heavy use without a restart, FF will become unresponsive in weird ways (refuse to open new tabs, or won't load URLs but already-loaded pages keep working, or won't allow you to drag links to other apps). It's a bit frustrating but a restart usually fixes that.