Well the feature development is certainly progressing - here is the tracking bug for it.

You can nowadays just test it in normal nightly without special build - it's extremely incomplete, but you can test it if you wish. It's tied to revorked sidebar which you need to enable in about:config.

Absolutely not. If anything, public officials would be the one group whose messaging I would understand being scanned so that the people can sort of keep them on check. But again, implementing such possibility that would still weaken security of everyone else as well so of course it should not actually be done.

Yes. I want to have access to both history and bookmarks on all my devices and send specific tabs to other devices. Sync makes these super convenient.

Right, but then you shouldn't be shocked to find out that a feature was removed because nobody seemed to be using it.

IIRC the old tab groups feature was eventually removed because telemetry showed that only very few people used it...

My first guess would be that this is caused by the website implementing its own navigation/history behavior using History API. That can easily mess things up, or at least not behave like you might want.

I think this really comes to what exactly you want to separate. You say "I often need to use two different profiles". Okay, why do you need to use separate profiles though? Maybe separate profiles are not a great solution in the first place for your purpose?

Firefox profiles are amazing because you can be sure that no data is shared between the two profiles (unless you sync them of course) - for whatever reason one might want that. But if you just need some session separation then containers would be a much better fit.

If a website has a compatible PWA manifest the there will be an item labelled "install" in the three-dot menu of Firefox in place of usual "add to homescreen" item.

Edit: There's a few other requirements as well for the website to be considered installable as PWA, such as it must have a registered service worker so it can work offline. But regardless, if the website provides all the requirements then it can just be installed straight from the menu.

Unfortunately by sending DNT you are merely suggesting to the server that you wish to not be tracked. There's no requirement for the server to actually care about you at all.

Now, if DNT were actually legally binding though - that would indeed be very cool.

Also, with mv3 extensions, the extensions that are not actively doing some work are not really "running" in the first place but are just waiting for some event to happen that they have previously told Firefox to inform them about, but there isn't any persistent execution context that is constantly running.

I believe one reason why extension support was not-fully enabled earlier was because mv2 extensions required persistent background context for each extension and that could cause issues if Android just decided to kill that process. But with mv3 the extensions are required to be able to be suspended and then woken up on demand.

None.

I don't think it's a good idea to take some huge collection of prefs and just apply them blindly.

Instead, make the changes that you actually want to do, so that you actually know what changes you are causing. If you want to put those into your user.js file then feel free, but in my opinion it's just better to change them in about:config directly - that is, unless you need to apply the exact same set of changes to multiple profiles.

Also, mobile Firefox has supported PWAs for a long time. I wouldn't say PWAs on desktop would be useless, but they make much more sense on mobile than on desktop.