Diversified to death?
Back when Netscape still was a thing, I tried out this Phoenix Milestone 16 preview build of what would eventually become Firefox after a few kerfuffles about who used which project name first. With the Netscape browser becoming less and less attractive after using it since its 4.x days, Firefox seemed like a breath of fresh air.
So what went wrong? I think that ironically one of the things that did Mozilla in was similar to what took out Netscape and Yahoo!: over-diversification, a lack of focus and a loss of marketshare on all fronts.
For those of us who used Firefox because it was not IE or Chrome, the 'Quantum' release of Firefox was a sad day, as it saw Mozilla aligning itself with Chrome in all but name. No more XUL, or the old-style extensions. Instead we got Chrome extensions and a browser that might as well have had the Chromium engine inside already. Maybe it's because Google is holding a lot of strings when it comes to Mozilla's existence that drove this. Maybe it was something else.
So now we have Phoenix^WFirebird^WFirefox, Thunderbird (-ish), Firefox OS, MDN, a new programming language, a whole new engine being written in said new language, a whole host of services (e.g. Pocket) trying to capitalise on the main projects, and now a Mozilla VPN service that rebrands an existing VPN service. What is Mozilla about again?