Of all the compile-to-languages, the one that strikes me as having the least merit is JSX. It's basically a ton of added complexity for the sake of what boils down to syntax. There are no real gains in terms of language semantics in JSX.

Blocking users from installing unsigned extensions without offering a cross-platform way to disable the feature brings minimal security benefits while concentrating power in the hands of the browser vendor. Not even Google is this heavy-handed, they allow installing local extensions in Chrome after users enable an option, although a warning is shown on browser restarts about the presence of external extensions, which can be dismissed.