I want to disable spell checking in multiline text input fields.

Opera help at
http://help.opera.com/Mac/12.10/en/spellchecker.html
is of no use, no matter what I do I cannot find a path that leads me to
Preferences > Advanced > Browsing

I have also checked the "Show advanced settings" box. I feel rather stupid here... how hard can it be...

BTW is it just me or is the forum engine really unable to search with more than one keyword? Every time I tried to search, e.g., for "spell checker" I got thrown back to Overview page, which makes no sense. I should get a sensible error message instead.

Opera 39.0.2256.48
OS X 10.11.5