Firefox is updated quite frequently which is of course a good thing. However whenever it is updated, it forces you to restart immediately, at least with the addons I have installed, which is just too annoying to me.
I am running Ubuntu with automatic updates enabled, so APT will periodically update FF in the background.
To disable automatic updates of just the firefox package, I discovered that I can hold it back like this:
sudo apt-mark hold firefox
Hopefully I’ll remember to update it manually, or maybe the FF developers will fix the issue at some point (although judging from online resources this is not likely because it’s not seen as a defect).