In my Fontforge version fontforge 11:21 UTC 24-Sep-2017 under File > Execute script the FF button is disabled. Is it not possible any more to execute native legacy scripts from within FF?
That version is very out of date.
While the legacy scripting language is recommended against, it still works at least as of the 20th Anniversary Release, 20201107, and there's no plan to remove it (I'm one of the maintainers).