> Mozilla will flip the switch on a completely new browser with the release of Firefox 57

It's not a completely new browser. It's still Firefox with some components swapped out, a lot of cruft taken out (due to cutting support for legacy extensions) and lots of individually small performance fixes (which were mainly made possible thanks to the recent rollout of multiprocess).

These new components have been taken from Servo, which is an actually new, written-from-scratch browser engine, but which is still far away from being production ready (might never be), so they can only retrofit finished components for now.

> Firefox 57 is the end of the road of a few Mozilla internal projects that aimed to fix most of Firefox's previous problems

Not the end of the road. Just a major milestone with PR drumrolls. More is very much already scheduled for the next few releases, the biggest of which will be WebRender.

> meaning developers of some Chrome extensions may soon port their add-ons to work on Firefox.

As is written directly below that, this API has been shipped in Firefox for a while already, so lots of Chrome extensions have already been ported.

> These users will be put in the unfortunate situation of having to choose between running Firefox without their favorite add-ons or finding a new browser where similar add-ons exist.

Or switching to Firefox 52 ESR, which will receive security updates until June 26, 2018 and continue to support these legacy extensions until then. Not a final solution, but it might bridge the gap until viable alternatives have been created.

Also, switching to a different browser will rarely make sense, as Firefox still is the most extensible browser by a long shot.

> Firefox 57 will also be the first Firefox version to support the new Quantum engine. Announced last year, the Quantum engine replaces some parts of the old Gecko engine with new components written in a mixture of Rust and C++.

"Quantum" is marketing kerfuffle from Mozilla. The engine is still called Gecko, it's just getting some components swapped out. Again, the components came from Servo, which is written in Rust. I am not aware of major components being included that have C++ code.

> Firefox 57 will include more Project Quantum code, such as Quantum Render, a brand new, GPU-optimized rendering pipeline based on Servo’s WebRender project

As I already mentioned above, WebRender is not in 57, but should hopefully land in the next few versions.

> Mozilla claims that all these changes have resulted in considerable speed boosts to Firefox's boot-up and browsing behavior, although this claims should be taken with a grain of salt, as all browser makers say the same thing when they launch a new version.

Or you could look at the fucking thing and notice that, oh hey, it is actually massively faster than previous Firefox versions. You don't even need benchmarks for that, it's clearly visible.

Some of the changes that are kind of counted into Quantum have been happening since Firefox 48 already, which is also why Mozilla's claim was that 57 is twice as fast as 52, so yeah, it won't be as significant of a difference going from 56 to 57, but it should still be relatively obvious.

I won't blame the author for misunderstandings or not being aware of every little detail, but to write something like that and not even test the two versions against each other is just lazy and bad journalism in every way.

> Also starting with Firefox 57, new Firefox installations will disable the search widget that used to appear in the top right corner of the old Firefox UI, an iconic part of the browser's old interface.

They did plan this, but apparently lots of people do actually use the search bar, so they've decided to put it back in by default.

> The planned UI changes are most likely to annoy some Firefox users because the Classic Theme Restorer Firefox add-on will also stop working, meaning users won't be able to control how their browser UI looks.

Or to 1) increase performance, the new UI is more efficient, 2) reduce maintenance cost, the new UI uses vector graphics for most things allowing it to be reused across OSs, 3) be more flexible, the vector graphics also allow for Mozilla to ship a Compact-mode and a Touch-mode out of the box, 4) look faster, the animations keep your brain busy and make it feel like things are faster, 5) help with marketing, a new UI is a far more visible change than a higher score on some obscure benchmark and will attract press coverage.

Besides that, Classic Theme Restorer is already broken anyways due to legacy extensions being removed.

And the new UI is actually more "classic" than Australis (square tabs, back/forward/refresh not glued to the URL-bar, dropdown-menu-like Hamburger-menu as opposed to the touch-optimized Hamburger menu in Australis etc.), so while Classic Theme Restorer did do lots more than that, the new UI should make a lot of users of CTR happy just by not being as unconventional as Australis.