Not every front, they gave us MDN and Rust, both of which will probably outlive them. KaiOS (the continuation of Firefox OS) is very popular in less developed areas of the world. Not that they managed to make anything off that.
MDN was a consolidation of several vendors’ web documentation efforts (I still remember Opera’s Web Fundamentals course fondly), which they collectively decided to put under Mozilla’s stewardship because surely Mozilla, among all of them, would maintain it neutrally and for the public benefit. It was a good run and Mozilla did do a good job at the maintenance for the last decade, but with their recent monetization efforts around MDN, I’m not hopeful for the future. (This is also why I’m incensed by Google’s web.dev—it’s not just the domain name, it’s that they are reneging on that old agreement.)
I was a cofounder of MDN (originally "DevMo"), and we did not use Opera or other materials, we used Netscape's DevEdge content which was released to us. You may be thinking of a later reformulation to unite with others outside Mozilla. See
Sorry, I probably did not phrase that well: I did not mean to imply that (what ultimately became) MDN was built on others’ materials. Rather, my impression was that other browser developers had agreed on taking down their own web documentation in favour of directing people to MDN, and that the Opera course (itself quite new at the time) was among the casualties.
Checking the Wayback Machine, looks like my subjective time was quite warped then: I had read the course around 2010 (which was actually called the Web Standards Curriculum[1,2], oops) and was sure it had been memory-holed with a redirect to MDN (along with the rest of Dev.Opera) when Presto was still alive (so before 2014), but it turns out that that did not happen[3] until 2018, matching your timeline.
Their handling of MDN has been disappointing. Laying off their staff, asking for unpaid contributors, and selling more advertising space was greedy business.
They're currently running a REDIS advertisement that looks like a critical error. The ad is a bright red toast!
_Speaking personally_, MDN is Mozilla's most valuable resource. It is the only resource I want to survive Moz's leadership.
