Well I was really brave and downloaded Firefox 5 (not very computer savvy) so that I could get the cool spell checker. But it doesn't work! I have checked under tools and it's there in the advanced tab, but I've just deliberately written a misspelled word and no red lines. I am so disappointed.
Edit, I just checked the help section, and I downloaded the English (UK) dictionary, and I now have red wiggly lines! But how do I get to somewhere that will give me some alternatives for the right spelling, or allow me to add a word? Right clicking isn't doing that. Still it's nice to have the lines.