He gains Mozilla's distribution model and audience, which allows users of Firefox to download add-ons from their browser's UI and updates automatically, rather than having to manually pull an extension file from a Github page for each new release and install it.
You gain $0 for uploading your Linux package to yum/apt/dnf as well, but you recognize that there's value in being able to install such packages easily through a well-curated repository, no?
Well you, the programmer, usually don't upload it. Some package maintainer does it since they want your software and ideally they should handle the bug reports for their package as well.
> allows users of Firefox to download add-ons from their browser's UI and updates automatically, rather than having to manually pull an extension file from a Github page for each new release and install it.
only because mozilla is gatekeeping that away otherwise.
For extensions which have full access to all websites, I appreciate that. That is one of the main reasons for ManifestV3 because not all extensions can be reviewed.
If you take into account small market share of Firefox and even smaller percentage of Firefox user needing uBOL then "audience" isn't anything important in this case. Perhaps this whole story will increase popularity of uBOL more...
What would he gain from submission to Mozilla? Either way he gains $0 for all the work he's done to improve the Internet for millions of people.