Rewrite links to known onion sites (especially for twitter)
Starting with a concrete example, this article publicizes twitter's new onion site. As is (perhaps unfortunately) increasingly common, the primary source it links to is a tweet using the clear-web twitter.com domain.
AFAIK the best way for a user to get to that link without visiting the clear-web twitter.com is to right-click, copy link, paste somewhere (maybe the url bar in a new tab), copy the onion address from somewhere else, and then finally use the link.
It'd be nice if TBB did this transparently, or maybe as a contextual option when right-clicking the original link. I realize this requires TBB to store clear domain -> onion domain mappings somewhere, but IIUC we're already doing that or in the process of doing it...?