[Springtime]

Firefox for many versions now has no way to disable update notification messages, which will repeatedly appear as a popup from the addressbar on every launch, unless one creates a new file with particular content.

Even if one wants a particular version for testing. Chromium doesn't do this ime. And this isn't to say it's a reason not to use FF but it is a counter-example to simply being able to dismiss something without it being annoying.

[nsagent]

Not just every launch, but also if you leave it long enough, it'll pop up again during the same session. This was what made me finally uninstall it.

And while Firefox has lots of flags and ways to tweak things like this, it's not straightforward and requires time to interrupt my workflow to address. Definitely not worth it for me on macOS. I might change my tune if I switch to Linux, but at that point I'll likely look into something like LibreWolf.