I didn't want to dilute the discussion of the Pale Moon/Firefox transition with talk of other browsers, but Opera (the original Opera) did not work successfully as a browser. It was based on their proprietary browser engine, Presto, and when users clamored for extensions to functionality, they were shot down. And down also went their popularity and, some would say, their usefulness.
So, there was much grumbling among the Opera devs regarding their browser was dying. The radical decision was made to move Opera to the WebKit browsing engine. Oh, yay. Another Chrome-like browsing experience...except without the Chrome-like extensions. Let's make a browser like Chrome & take everything that users love about Chrome...and not use those parts.
This is very confused and mostly wrong.
Opera was always at the forefront of browser innovation and a lot of their features were copied by the big guys. The problem they faced is that it required simply too many resources for a relatively small company to compete with the big guys (Microsoft, Google, Mozilla, Apple) and they did not have the clout to get their cross-platform Presto engine considered in the adoption of standards.
What they did was to stop development of Presto (which remains licensed to other software companies and apparently still maintained on various platforms) and start building a new browser based on the Chromium Blink rendering engine that powers the Chrome browser and is developed and maintained by Google. This allows Opera to spend their own resources on browser UI while keeping up-to-date on security and standards, courtesy of Google's vastly greater resources.
I've used Opera since 2000 and loved many features that have yet to be added to the Chromium version, but there is no doubt that the company made the right decision to survive. I've been using the Chromium Opera for about a year now and even though it still has some rough edges, it has become my favorite browser for Web surfing, although Firefox is still my default for many purposes, particularly if they involve printing or page capture.
I'd guess that the Mozilla Foundation is also taking a hard look at the future and that their announced plans, while upsetting to many of us who depend on current Firefox extensions, are part of a strategy they hope will keep them around for the next decade. Given the power wielded by Microsoft, Google and Apple, that's probably the only way to go for most independents.