Turning off auto-correction in Firefox

Anyone who knows how to do this? Since I use Swedish FF almost every english word I write (every single one so far... no, wait, it recognizes 'so' and 'far') gets red underlining telling me it's not been spelt correctly. This is starting to get really old and I've been using my new FF for ten minutes. So, how to turn it off?

Übereil

Tools —> Options —> Advanced —> General —> Browsing — "Check my spelling as I type"

I'm typing mostly in English and it doesn't bother me too much when I type in German, but yeah, it probably only makes sense to have it activated when you use only one language most of the time.

Edit: Alternatively you can try to install an additional English dictionary.

Thank you!

Übereil