It's funny because Firefox has been pushing their login thing pretty hard (the yellow "oh no" exclamation mark icon if you're not logged in, the account icon that keeps placing itself back onto my toolbar, occasional full-page ad/nag screen, ...).
Not only that, but on new installs and after some updates Firefox nags you to sign up whenever it can, for instance when you log into a website - right after you save the password it will show some animated crap in the address bar to nag you to "Sign in to sync..."
I just opened Firefox (on Linux no less) to confirm every single one of these things.
Chrome (my default browser) actually nags me less and in less annoying ways.
Because they just log you in without asking, as noted in the comment you're replying to. It also has more severe implications in Chrome privacy-wise, directly linking your Chrome profile with all kinds of other privacy-sensitive Google services. Since Google is in the business of making money from the data they have on you (and hence collects as much as it can), I'd be much more concerned about this than I am about my Firefox account.
I see no way to opt out of all the nags Firefox gives me.
The very first screen on first open nags you to signup, the top menu item is “Sign in to Firefox”, there’s a notification dot on the user icon with the Sign in nag there, the Pocket button asks you to sign in and after I log into a website I immediately get an animated recommendation nag to also sign in to Firefox.
It’s absolutely 100% plastered around the Firefox UI.
https://blog.mozilla.org/services/2014/05/08/firefox-account...
I don't particularly care whether nagware functionality is benign or not.
You might not consider that use case important, but I wouldn't call it questionable.
It's the kind of "oops haha just a mistake that we did the bad thing again" shenanigans that Mozilla employees complain about Google doing.
On the other hand I find Pocket a much more questionable addition.