If I could time travel into the past, in addition to preventing all the bad things (e.g. Young Sheldon), I might have told Yahoo they should flex some financial muscle while they still had relevance and worked to mobilize (no pun intended) developer time, energy, etc and perhaps even provide a baseline ecosystem of stock apps to support FirefoxOS.
We did guess it. Google were already past their “don’t be evil” days in 2013. They were possibly better than other companies of similar scale, but the decline was already clearly beginning. People had long warned that Google could not be trusted to keep Android open in the long term, that eventually their benevolence would fade. A good chunk of the enthusiasm around Firefox OS was in breaking the duopoly and the idea of a platform that would be much harder to lock down.
But on the other hand progress was quite good. Back in the days I was maintaining unofficial images for Alcatel Fire. Each version was a little bit faster, but you really can't do much when the whole OS is a browser running on a device with with 256MB of RAM and a single core CPU.
Today, we have Mobian, postmarketOS, PureOS and many more GNU/Linux OSes for smartphones.
If I want to interact with modern society, I have to use banking apps, the NHS app, WhatsApp, numerous IoT apps... The list is endless. Many of these will refuse to run on rooted phones.
Google and Apple won. We can learn from this and hope the next big thing to come along has some competition from the truly open source side of computing.
The two places it's mind boggling that Mozilla doesn't have a product are (1) identity (especially as a provider to 3rd parties) and (2) instant messaging (especially on mobile).
They were important 10 years ago, they're more important today, and the existing providers all have huge privacy concerns.
Nothing says you have to track users, if you're not looking to optimize ad monetization per user.
And I daresay there are a fair number of companies who would love to get even blind exposure to Mozilla's userbase.
Doesn't Mozilla have their own Matrix server?