It's an open source product, in case you have concern about possibility of malicious code embedded within it.
At least there is no such indication so far from Mozilla :(
In India, the share of Linux desktop became double just within one year (from 8% to 16%). I only hope this data is right.
https://gs.statcounter.com/os-market-share/desktop/india/#monthly-202301-202407
I moved to Mozilla Thunderbird long ago https://www.thunderbird.net/en-US/
UX is a very subjective matter.
Bad news is that it is not clear at this point whether Mozilla is going to go forward with the implementation. A post on Reddit by one of the project members suggests that the build is a "rough proof-of-concept". Some features tested in the build "did not survive". It is unclear which did not, as they are not mentioned. Mozilla is, however, implementing those that survived the cut into Firefox. Again, the poster does not mention which those are. It is also not verified that the poster is actually a member of the project team, so take this with a grain of salt as well.
All of these are signs of persistent threat actors aka State sponsor hacker. Though the real motive we would never know as it's now a failed project.
Source: https://turnoff.us/
There is a work-in-progress version of Firefox for iOS with Gecko engine.
But, there is also a challenge that Mozilla is facing as Apple is still trying to make life of developers of other browsers as difficult as possible.
So, not sure how the whole thing will turn out.
Ubuntu.
Why? - I guess I'm too lazy for distro hopping now :(
Besides, this was the 1st Linux distro I tried back in 2005. After the usual ditro hopping phase was over, I settled on it; somehow (irrespective of snap and other controversies) I feel at home.