Bug: "Firefox is being updated by another instance" on all instances at the same time

[noo]

I regularly run several Firefox profiles in parallel. Every once in a while, it seems the update logic gets confused and every window says "Firefox is being updated by another instance", with none being able to (even manually!) check for updates.

It would be great to have a different way of fixing that situation that doesn't require closing & reopening all instances and hoping it doesn't happen again…