1. Tell us the link to such a page, and clearly tell what strange it is you see on the page.
2. Tell us how this same page shows in IE (what version) with different settings.
3. Tell us the same for Google Chrome.
Alt-155 (or alt-024 is just a standard scandinavian character (an O with a slash through it). There's nothing special about it and it certainly isn't an html-character (in fact, there are no such things as html-characters).
4. 5. 6. Tell us how the name of the town on http://en.wikipedia.org/wiki/Bod%C3%B8 looks for these same settings in these same browsers (don't you love Unicode?).
I don't think this is a Firefox problem. So it's up to you to prove that it is, by showing Firefox behaves differently from IE and Chrome.
I'm running Firefox 3.5.9 on Windows 7. When I visit sites, some of the headings are broken, unreadable and looks like HTML characters (the kind when you press ALT + 155 or whatever). I've looked at the languages option and everything seems to be okay. It works when I uncheck allow website to use it's own font.
Can anyone help me with this? Much appreciated...thank you.