Hmm, I feel a bit queasy about this for a few reasons:

* Will `window.opener` be truthy if the user isn't actually coming from the bookmarklet? I can imagine some potential scenarios but I also don't know a ton about `window.opener` and `window.dialogArguments`. Is there anything wrong with the bookmarklet actually opening the `/update` URL with a `from_bookmarklet=1` in the querystring, and simply detecting based on that?

* Line 9 is clobbering any existing action that might have been set on the form. Currently, that's fine, but I'm concerned about this functionality breaking if that form action ever changes. Instead of doing this, what if we added a `<input type="hidden" name="from_bookmarklet" value="1">` to the form POST data?