Firefox is not dead, but it is on a downward trend.
- Management goals of Moz don't look good
- Funding for Moz is greatly controlled by their competitor Google
- Google and other groups keep pushing web standards to be more complex & changing, so that no new players can't easily enter the market
- Apple remains the only strong independent with their forcing of Webkit on many of their devices.
There are smaller groups working on their own browser engines (
Netsurf,
Flow) and forks of Mozilla's Gecko (
Seamonkey,
Palemoon); however these are going for smaller market appeal (unless something dramatically changes in the browser landscape, eg a freeze or culling of new crazy vendor-driven standards).
At the end of the day: whilst browsers don't cost users actual money, it's still a cut-throat competitive market about control and money.
Google wants everyone on Chrome so they can collect as much data and market as much as possible. If not chrome, then they want everyone at least on a chromium engine so they can control the direction of web standards and so make it harder for competitors to regain market & mind share. A user monopoly plays directly into their profit, they're a business.
Apple wants to keep all of this off their mobile devices, so they force Webkit (even if your browser claims a different name it's still webkit under the hood, just reskinned. You have to jailbreak to get around this). This keeps them with more control over their platform and devices, which is a long term strategy to avoid other companies finding ways of profiting on their devices without Apple agreeing/getting a cut.
Firefox wants to exist for a variety of reasons. Many of the devs and supporters think it's the right thing to do for the freedom of the web and to keep user's safe. Unfortunately the leadership also seems to want to make it a viable business of its own (without selling user data). I don't think Google will ever let them do that, but is more than happy for them to hurt themselves trying. They spent millions of USD acquiring the pocket addon and now they're planning to do similar branching-out.