I want to use the built in Mac OS X spell checker in Firefox, instead of the one that Firefox ships with. I have a lot of words I've told it to learn and in general, it's just more accurate (today, Firefox's spellchecker said that "immersive" wasn't a word, even though Mac OS X's spellchecker confirms that it actually is). I've tried going to Preferences -> Advanced and unchecking "Check my spelling as I type", but that doesn't make Firefox default to the Mac OS X spellchecker. I tried Right-Clicking in the text field and choosing Languages -> Add Dictionaries…, but that doesn't let me add the Mac OS X spellchecker as a dictionary. Is there any way at all that I can make Firefox use the superior spellchecker built into Mac OS X?