I think the "Why?" section's conclusions are off the mark. It basically blames Google's advertising of Chrome for Firefox's decline, and even goes so far as to say "Firefox’s decline is not an engineering problem."
While I don't doubt that Google's advertising of Chrome has drawn away some Firefox users, I also don't think that we can ignore or deny the many controversial changes to Firefox that have likely had an impact, too.
Just off of the top of my head I can think of things like:
* Frequent breakage of extensions when first switching to the more rapid release schedule.
* Frequent and disruptive UI changes that didn't bring users much benefit, such as Australis.
* Removing the ability to easily disable JavaScript.
* Taking many years to get multiprocess support working. (Not that I'm suggesting they should have rushed it, of course.)
* The inclusion of Pocket and Hello.
* Sponsored tiles.
* Users who report experiencing poor performance and high memory usage.
* Disruption caused by requiring signed extensions.
* The removal of support for OSes or OS releases that are moderately older, but still do have active users.
I'm sure there are others that I'm forgetting.
Even if they seem minor, those are the kinds of things that can cause users to switch away from Firefox, or not even start using it in the first place. Losing a small number of users for a variety of minor reasons can add up very quickly, as well. Furthermore, those issues don't really have anything to do with Google or Chrome.
While I don't doubt that Google's advertising of Chrome has drawn away some Firefox users, I also don't think that we can ignore or deny the many controversial changes to Firefox that have likely had an impact, too.
Just off of the top of my head I can think of things like:
* Frequent breakage of extensions when first switching to the more rapid release schedule.
* Frequent and disruptive UI changes that didn't bring users much benefit, such as Australis.
* Removing the ability to easily disable JavaScript.
* Taking many years to get multiprocess support working. (Not that I'm suggesting they should have rushed it, of course.)
* The inclusion of Pocket and Hello.
* Sponsored tiles.
* Users who report experiencing poor performance and high memory usage.
* Disruption caused by requiring signed extensions.
* The removal of support for OSes or OS releases that are moderately older, but still do have active users.
I'm sure there are others that I'm forgetting.
Even if they seem minor, those are the kinds of things that can cause users to switch away from Firefox, or not even start using it in the first place. Losing a small number of users for a variety of minor reasons can add up very quickly, as well. Furthermore, those issues don't really have anything to do with Google or Chrome.