I tried deleting the symlinks en-US.aff and en-US.dic in /usr/share/myspell/dicts and restart Firefox, but there are still two languages: "en_US" and "English / United States"
/usr/share/myspell/dicts$ ls
backup DicOOo.sxw en_US.aff en_US.dic hyph_en_US.dic
I tried deleting the symlinks en-US.aff and en-US.dic in /usr/share/ myspell/ dicts and restart Firefox, but there are still two languages: "en_US" and "English / United States"
/usr/share/ myspell/ dicts$ ls
backup DicOOo.sxw en_US.aff en_US.dic hyph_en_US.dic