Excuse my stupid question, but do "favorite" and "favourite" mean the same thing?
Yes, they mean the same thing. From Wiktionary's entry on favorite:
- (Commonwealth English) favourite
They are two different spellings for the same word: favorite is used in American English, favourite in all other varieties of English.
The same also goes for words such as behaviour/behavior, colour/color, etc. In these case, the -u- can be left out because it's silent, the same however cannot be said for other words like pour and devour, which do not become por and devor, because spelling them like this would also alter their pronunciation.