This has never happened to me.
But I cut Mozilla some slack for it since this is a pretty unusual setup and the Developer Edition is updating quite a lot compared to the release branch and it doesn't happen all the time.
example : a cctv kiosk I have just sits on a URL all day.
It updates silently and breaks the browser sometimes a few times a month, facilitating remote administration to reset.
The other lovely behavior is when after an update the tab to show update notes is prioritized upon browser auto-restart -- thus covering up the cctv kiosk tab with something advertising firefox changes.
Firefox is getting harder to love, (thankfully?) so is the competition in most cases.
I mean, you can kind of use Electron for this, but it's not designed to be used this way (i.e. to be used un-customized as a long-running service with hot updates.) It's designed as an SDK for developers to produce apps with, not as an app in-and-of itself.
https://fluidapp.com/ exists, but it's not multiplatform, and it still doesn't address the needs of the embedded market either.
https://support.mozilla.org/en-US/kb/firefox-enterprise-kios...
"Firefox has just been updated in the background. Click Restart Firefox to complete the update."
It would at least be a minor improvement if they'd open a new tab to show you that information. Instead you're refreshing the page wasting everyone's time because it doesn't always tell you that's what's going on.
If you use Mozilla's build of Firefox and it's built-in update system I think this won't happen.
(Disclosure: I work for Mozilla but not on this)