Mozilla were ruined by big Google checks. How they could let this opportunity slip while electron became the ui for every major desktop app… such a shame.
Personally, I feel Mozilla did not market XUL[1] enough. Had they done that, it could have become what Electron is today, with a native look and feel, and with a much reduced footprint while still offering a JS-based runtime for applications.
They had support for PWA in 2021, before they pulled it. Hard to see this is anything other than a concession to its biggest funder, Google. Chrome, Edge and Safari all support installing PWAs, while FF, the biggest beneficiary of such a change, intentionally gimped theirs.
[1] https://en.wikipedia.org/wiki/XUL