Turn off grammar check on yahoo mail/firefox?

-Every time I write a yahoo mail in my native language most of the words are highlighted (obviously), but since yahoo mail came up with the new style, the highlights are a lot more obtrusive and I find it really difficult to read what I write. I am not sure if Firefox or yahoo mail is the cause of this (I'd guess that firefox) and I haven't been able to find out how to turn off the grammar check.

Any help?



Thank you