1) Mozilla isn't retarded. They've done market research on this.
For example, in Sep. 2015 around 40% of users did not use any extensions at all. Another sizeable number of users is going to have their ad blocker and nothing else. Even with 2, 3 or 4 extensions, it's unlikely that you're going to experience a breakage, and if you do, it's likely that you'll find a replacement.
Average users rarely use unpopular extensions and popular ones either are maintained or will have a replacement made. There are some semi-popular ones that currently can't yet be fully recreated, but those are the types of extensions that change so much about the browser that average users won't be using them anyways.
2) Users aren't retarded. I know, we like to act like they are, but only the most cynical are going to switch browsers, because of this. Out of spite. It does not make any sense to switch to a different browser, just because the browser that you're used to has become different. Nor does it make sense to switch to Chrome, which is still by far less extensible than Firefox 57, just because Firefox has become somewhat less extensible.
3) The core of the API is more than stable. It's Chrome's extension API, that's been battle-tested in Chrome for years. Most extension developers will not need more than that. And it's most definitely not missing a ton of function, especially not things that non-power-users need.
4) Their market share is not anymore shrinking. It's been growing again since the release of Firefox 48. That was the release which shipped the first iteration of multiprocess. They could not have shipped multiprocess as early as that, if they did not know legacy extensions to be deprecated now with 57. Because the majority of legacy extensions are not multiprocess-compatible and neither would have been updated to be.
AMO would be reverse Russian Roulette where only roughly 1 out of 6 extensions will not kill your performance. That's just as well something you can't expect average users to understand and it would be like that for the next few years still.
So, yeah, they did rush this, but it was to save their market share. Had it continued to drop like in the half year before Firefox 48, we'd now be deep into negative user numbers.
> Even with 2, 3 or 4 extensions, it's unlikely that you're going to experience a breakage, and if you do, it's likely that you'll find a replacement.
This is simply not true as there had been many popular UI-centric extensions that just can't be replicated as webextensions due to lack of API support. "Advanced UI features belong in extensions, not in main" had been the Firefox mantra for many years and negativity about 57 is the logical consequence.
Which are the type of extensions that change so much about the browser that average users just won't use them.
When I discovered Classic Theme Restorer, Tab Mix Plus and similar, I was already a semi-pro user and I still found them intimidating.
There were a lot of checkboxes and they changed around a lot of things and I didn't yet know how to create a separate Firefox profile where I could've actually just wildly tried different options without the fear of something breaking irreversibly.
For example, in Sep. 2015 around 40% of users did not use any extensions at all. Another sizeable number of users is going to have their ad blocker and nothing else. Even with 2, 3 or 4 extensions, it's unlikely that you're going to experience a breakage, and if you do, it's likely that you'll find a replacement.
Average users rarely use unpopular extensions and popular ones either are maintained or will have a replacement made. There are some semi-popular ones that currently can't yet be fully recreated, but those are the types of extensions that change so much about the browser that average users won't be using them anyways.
2) Users aren't retarded. I know, we like to act like they are, but only the most cynical are going to switch browsers, because of this. Out of spite. It does not make any sense to switch to a different browser, just because the browser that you're used to has become different. Nor does it make sense to switch to Chrome, which is still by far less extensible than Firefox 57, just because Firefox has become somewhat less extensible.
3) The core of the API is more than stable. It's Chrome's extension API, that's been battle-tested in Chrome for years. Most extension developers will not need more than that. And it's most definitely not missing a ton of function, especially not things that non-power-users need.
4) Their market share is not anymore shrinking. It's been growing again since the release of Firefox 48. That was the release which shipped the first iteration of multiprocess. They could not have shipped multiprocess as early as that, if they did not know legacy extensions to be deprecated now with 57. Because the majority of legacy extensions are not multiprocess-compatible and neither would have been updated to be.
AMO would be reverse Russian Roulette where only roughly 1 out of 6 extensions will not kill your performance. That's just as well something you can't expect average users to understand and it would be like that for the next few years still.
So, yeah, they did rush this, but it was to save their market share. Had it continued to drop like in the half year before Firefox 48, we'd now be deep into negative user numbers.