We had a concrete business opportunity with several high volume customers lined up. The big driver was 4G transition. To convert legacy 3G bands to 4G carriers have to move feature phones onto an LTE capable platform. KaiOS managed to capture the same opportunity.
The main reason that Firefox OS was shut down was that management wanted to focus on western markets and desktop, which was and is the only revenue driver. I left since I didn't see any growth or opportunity or interesting problems to solve in that Venn diagram.
Are you in the process of trying to get it reinstated, or not yet? (The ACLU letter doesn't seem to include a demand for reinstating it, but I guess you'd be approaching it in some other way)
I tried my best to get the tracking protection patch shipped after you left. There were no realistic technical concerns with it. The entire engineering team wanted to enable it. The patch was ready for prime time. I was overruled for non-technical reasons. I left not too long after.
A comment said the same and I added a note to the text. If you have concrete data happy to update charts. Pull request welcome :) All code and data for charts on github.
I had the opposite experience. I used Firefox the last 48 hours on Mac and it works really well. I can't find a reason to not use it, but also no reason to use it. Commodity products. I think this is the choice most users face. Add a lot of marketing dollars and defaults on Android and you can explain Chrome's growth curve.