While I usually don't highlight grammatical mistakes (as I am not the most skilled in the English), one has the option "to favorite a post" in Stack Exchange sites. As far as I know, one can either "favor a post", or "make a post a favorite" because favorite is not a verb but a noun.
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Verbing nouns is a fairly common occurrence, especially in the tech sector.
I don't think it's meant to be grammatical, but it is meant to be descriptive while also being succinct. "Favorite a post" is certainly briefer than "mark a question as a Favorite".
I do wonder if we're not doing our non-native English speaking users a disservice by deviating from accepted grammar, though.
Verbing is a common feature of the English language. It's one of the things that makes it so flexible and easy to learn for a foreigner - any word can basically be of any type. So it's not only verbing that's possible, but also nounifying and making words more adverbish, etc.
Having said that, this laxidasical approach to the language does have its drawbacks, but I'm in favour of it -- if only because it made some of George Bush's speeches so much more entertaining to listen to, with words like "misunderestimate"! ‡