Most of the comments so far are variations on the same theme... Firefox's product management has not been great. If you want your product to win in the marketplace, it has to serve end-users better than the competing alternatives. Nothing should make it into the product if it doesn't improve the end-user experience. I use Firefox because plugins like NoScript and Adblock Plus work in Firefox. But there are many strange problems that we Firefox users always have to contend with. For example, if I have EVER had a secure connection with a domain (Netflix.com), Firefox will INSIST that I always have a secure connection with that domain, and I can't browse non HTTPS pages on that domain (like the Netflix Tech blog). That's not security. That's just stupid. I'm just trying to browse a static web page... I'm not posting any information, or entering a password or credit card info on that page.
Mozilla also gets religious with respect to video codecs. Again... just stupid. Tens of thousands of companies worldwide want to support newer industry standards, like HEVC, but Mozilla in their infinite religious wisdom thinks that HEVC should fail and VP9 should succeed, so even when a website wants to deliver HEVC video, and the consumer has an HEVC capable device, Mozilla believes that Firefox should block the HEVC video from passing through to the device. You can have whatever political beliefs you want, and you can try to influence the discussion, but when the market has spoken, you need to listen. Any browser vendor that thinks they can leverage their installed base and market power to force their worldview on the end-users will ultimately fail. This is why Mozilla succeeded in the first place - because Microsoft was inflexible and not listening to the needs of end users.