In the Apple store, those "Firefox", "Chrome" and "Opera" are just skins over Safari. Apple doesn't allow anyone to provide a different rendering engine.

I don't think that Microsoft "banned Firefox", but instead that the APIs that can be used by the App Store apps are quite limited and as Mozilla is struggling to avoid death they didn't try to waste resources working in something that no one would use.

I'm sorry to burst your bubble, but Firefox uses Gecko, and Chrome and Opera use Blink. Safari is the only mainstream browser that keeps using Webkit.
So you really need to test all of them and checking that Edge works as expected is not too hard (really, most of the time Edge works out of the box)

You use BrowserStack for free https://developer.microsoft.co... or you download one of the many VM that Microsoft provides for free https://developer.microsoft.co...

Now, please tell me how to test that "cross-platform" Safari for both Mac and iOS without paying huge amounts to Apple or a monthly fee to BrowserStack

If you want an ad blocker, then you should install the proper extension: https://www.microsoft.com/en-u...

No?
I would bet that my instance of Brave takes care quite well of the ads. And Brendan Eich is one of the persons behind it, so I'm happy if this is the way to show Firefox that they committed suicide by supporting the justice warriors instead of its CEO.

I also used to use Firefox on my phone, but it was really slow. Since some months ago I'm using Brave which uses the Chrome engine, but it includes privacy protection against ads and trackers and I haven't missed Firefox not even one moment.

You should test Brave.
It has the adblock built in and it starts loading the pages as soon as click on the links, so you don't have to wait for redirections and all the stuff to be downloaded while you keep on reading other stuff

I don't remember the last time that Firefox crashed for me although I use it daily, but on the other hand I use Chrome just for testing and I've seen it crash at least twice last week.

What they have "released" is just the Aurora channel with the Dev Tools theme covering all the browser.

Everything else seems to be just the same that it used to be, the only improvement is the ability to run it side by side with another Firefox profile but if you used work with Aurora like I did, all this means that you must go back to the beta channel to keep an usable Firefox with a normal UI (after applying the Classic Theme Restorer)

Their "mobile emulator" is quite simple, I don't understand why anyone would like to use it to debug Chrome on Android instead of using Chrome on their computer as it has better tools and surely it will always be integrated better.

And for CSS tweaking I prefer to use Firebug or even the IE11 dev. tools thanks to its great CSS Changes pane.

I will not trust in Chrome until they stop adding their plugin into Firefox.

If they care so much about what's run inside Chrome, why do they inject their Google Updater into Firefox and put their update code in a bazillion places?

Yes, they say that it's mean to always have the latest version available, but if I'm not using it daily, why should I waste CPU cicles and bandwith trying to upgrade it until I use it?

I have Chrome installed only because I need to use it for testing, but I strongly dislike its UI and its behavior, I just wish that it would be a normal program that only tries to update itself when I run it.

I use Firefox daily on my Nexus 7 and I think that I haven't ever seen it crash.

When the Jelly Bean 4.2 was released Firefox was one of the apps that required an upgrade, but even then I didn't had a problem because I use the beta so by the time that Google sent the OTA to my tablet Firefox was already updated.

Uh?
Besides their own branded tablets, have you checked which is the manufacturer of the Nexus 10 monster (2560x1600 screen, 16Gb at 400$) that comes out tomorrow?

So your apps are returned in Android and you blame that on piracy.

But the fact is that the user only has 15 minutes to return the app and if he plans to pirate it, why would he bother on buying it at all?,
Pirates won't ever bother inserting their credit card on Google Play and go straight to the alternative markets and when people are returning your app after just 15 minutes then it's clear that there's something wrong with your app and you shouldn't blame anyone else but you about that

Are your apps those that are simple ports from iOS and that lacks total respect for the Android UI and environment?
It's funny to see how people claim how iOS is much more stylish and when they port an app to Android they try to force such iOS UI and of course people rejects those abominations