I used Cacher (and its predecessor GistBox) for about a year, and found it to be a good snippet manager, although not my favorite. One of its strong points is that it syncs with GitHub Gists.
I have had very limited experience with this FF Extension, so I can't recommend it one way or the other, but it might provide a decent tool to quickly get code on a FF page. You can also save any selected text using the Cacher context menu. Select a the text, then: Right-click -> Cacher -> Save Selection as Snippet