Bookmark a page which has already been bookmarked. The resulting dialog ("A
bookmark titled %s already exists for this page." needs much love:

- The entire message is wrapped in <big></big>
- The bookmark title is wrapped in <b></b>
- The message is unclear: what if I wanted to write the same bookmark with two
different names?
- The text is not selectable
- "titled" isn't a very appropriate verb (it's most commonly used as a noun). At
the very least, "entitled" would be better.

Maybe the dialog should be removed altogether. Instead there would just be the
'Add Bookmark' dialog and the relevant topics would already be selected.