It's quite weird that Google seems to try to crawl some Facebook content, which makes me get a warning. How do I avoid this?
This alert isn't relevant for your site's rating and ranking. Google absolutely realizes, that it crawls a third party ressource, and Google knows the web situation profound enough to understand, that you don't control crawling of scripts hosted by Facebook ;)
But with the very high paranoia level you could host Facebook scripts locally and allow their crawling. Some webmasters are doing so, because of paranoia or because of performance - i've read reports about achievings of performance gains (because of less requests through the web). But this is personally for me rather a kind of religious question - i guess, performance gains are in the scope of