Turn off grammar correction in a contenteditable div in FireFox

Question

I have contenteditable div with text on it. In firefox, there is some kind of grammar correction which underlines the text with red marking. How can I turn it off?

Answer 1

According to MDN:

Starting in Gecko 9.0 (Firefox 9.0 / Thunderbird 9.0 / SeaMonkey 2.6), the spell checker uses the element's lang attribute to determine the default spell checker language. If doesn't have a lang attribute, that attribute is searched each successive parent element and upward toward the root node until one is found.

So to disable spellcheck, not only do I add spellcheck="false", but I also add a lang tag with a dictionary not found on the users computer.

This should work on most systems outside of Kronos.