Let me explain: I've used Firefox since the beginning (and Navigator before that). I like Mozilla and I agree that most of the changes that they've done internally in quantum were kind of necessary (although many could have been handled better).
However, along the way, they've broken the way many people use Firefox and the only answer the frustrated users seem to get is "but it's fast".
They've changed the UI to be similar to Chrome, to the point where the reload button is not where it used to be. But it's fast.
They've broken the extensibility, which was (at least for me) the main reason to use Firefox instead of Chrome, Chromium or any of the others. You could do things in Firefox that the others couldn't even dream of. But it's fast.
While doing this, they've alienated plenty of plugin developers, people who loved the Firefox ecosystem, some of which have had to rewrite their plugins thrice already (with some being told to, essentially, "bugger off"). But it's fast.
As far as I can tell, it's using more resources in MacOS than the old version, at least the processor runs hotter and the fans kick in more often. I've had issues with the CPU use sky-rocketing, but I believe that has more to do with opening multiple tabs quickly rather than with one specific page. But it's fast.
Honestly, I haven't noticed any major changes in speed in Quantum (it's a bit snappier, that's it) and was happy enough with it's previous performance. IMHO what we've lost is not worth what we've gained.
I'd move to other browser, but which one? None of the main ones have the things I liked about Firefox and I don't really see most of the forks being able to keep up the pace. I guess that I'll stay, hoping that the things I love about Firefox will eventually come back.
While it's possible to re-implement Tab Groups with the new API, extensions like SQLite manager [1] will never work again.
I wrote instructions [2] on how to restore lost tab groups after update (involves downgrading and disabling updates).
[1] https://addons.mozilla.org/en-US/firefox/addon/sqlite-manage... [2] https://github.com/Quicksaver/Tab-Groups/issues/560#issuecom...
It's mainly more secure by having most things sandboxed now. That requires Firefox to be executed in the new multiprocess architecture and for that they would have had to kill off at least those legacy extensions that are not multiprocess-compatible, which was essentially all of them as well.
Also, yes, multiprocess did also most definitely play into performance. But we're not talking about the difference between 56 to 57, it's rather the difference between 47 to 57. Because 48 already introduced multiprocess, even though as a user you were still perfectly capable of installing a multiprocess-incompatible extension, which then caused Firefox to drop out of multiprocess whenever that extension became active. A completely intransparent way for users to completely kill off their performance.
Lastly, you don't claim that what Mozilla did on a whole is wrong, but yeah, just to point it out anyways: They are somewhat throwing power users under the bus right now. They don't enjoy doing it (essentially all Mozilla devs just as well are Firefox power users), but they do want to save their market share in order to still have a word when it comes to web standards and the market share just isn't made out of power users.
Around 40% of Firefox users in Sep. 2015 did not have any extensions installed. Another sizeable chunk will have their ad blocker and nothing else. This release won't affect these users negatively at all. They'll just get the better performance and the better security.
The only thing I heard from my parents was my mum asking me, if it's normal that Firefox looks different now. Maybe there'll be some confusion with the new Library-button, but other than that, it's just yet another browser-UI. They know this.
And Tree Tabs [1] seems to be doing something functional into the direction of tab groups. Maybe that works for you...
[1]: https://addons.mozilla.org/en-US/firefox/addon/tree-tabs/