You seriously think that removing the ability to disable javascript (well, not really, you still can - just not as easily) is in any way a factor? Which other browser makes this easier?

Pocket? Hello? Really?

Firefox memory usage has for years used less memory; basically since its inception. Apparently it's no different now: https://www.gizmodo.com.au/2017/03/whos-winning-the-browser-...

e10s? Come on, give me a break. I bet the vast majority of users have never heard of it, and of the others, most don't know what it's about to any useful degree, and of those that understand this feature, most probably wouldn't know the details of how the various multiprocess implementations actually compare. A vanishingly small proportion of the user base know of this feature, understand it enough, can compare this to other browsers, and then have a strong enough opinion to affect browser choice (and frankly, it's not obvious multiprocess is actually that great of an idea in the first place if you really do know what you're talking about - not one of the browsers actually separates every tab into a separate browser - for a reason!)

As to OS support - firefox still is the last browser to support XP, so I'm not sure what you're referring to. Version 52 was the last one; but that's on an extended support cycle until june 2018, which AFAICT is more than two years later than chrome's last v50. Microsoft hasn't "supported" XP with any reasonable browser... well, not ever (the highest IE version was 9!), and it hasn't supported the OS at all even with security patches for years (with certain notable exceptions).

As to disruptions caused by signed extensions - so that's why the appstore has failed and nobody is using windows anymore? I get it's annoying, but this is a pattern that's recurring all over the industry, and has for many years before FF made this step. If anything, I think it's more plausible FF is being punished because it was too slow to ban unsigned extensions! Because poor experiences based on bad or even malicious extensions do reflect on FF. And for that matter, signing isn't the real issue, it's add-on sandboxing/threading. Chrome got this "more" right, in that it's less likely for an novice extension author to accidentally bring chrome to a grinding halt. But precisely this feature is still causing lots of addon breakage because FF has not yet completely dumped the old, problematic add-on API, presumably because users really hate losing their cherished extensions (and for a reason). I've witnessed several addons that have chrome+FF equivalents where perf issues occured only in FF - which may have been the addon author's "fault" - but that's a really poor excuse.

Poor perf, and the expectation of poor perf sound like more reasonable guesses, but even there I'm not convinced this actually matters as much as you'd hope. Still, that's at least something. But then, the number of people you see working with unworkably slow setups for all kinds of reasons that apparently don't care enough to switch products suggests that even abominable perf isn't necessarily very impactful. Maybe this matters indirectly; in that power users that care influence others in their choices.