[Greasemonkey] Greasemonkey or Extension to use Spellchecker

[abhijeet saran]

Hi,

Trying to learn the ropes. I want text in a selected div to be
underlined. Wondering if I can use a greasemonkey script or need to
learn how to write an extension? From Mozdev Article

gSpellCheckEngine = Components.classes["@mozilla.org/spellchecker/myspell;1"]
.getService(Components.interfaces.mozISpellCheckingEngine);
gSpellCheckEngine.dictionary = 'en-US';

if (gSpellCheckEngine.check("kat")) {
// It's spelled correctly
}
else {
// It's spelled incorrectly
}

I'd really appreciate if someone could just tell me how to call the function!