Bug 1049569 - Sanitize e.me app url results. r=francisco

e.me app result urls often miss the trailing slash. Sanitize them so we get better bookmarking behaviour in the system browser.
Right now we are leaving a case where the promise can fail, in that case we should disable as well the use of the bookmark, IMHO, since it means there is something wrong with the bookmarks datastore.

In that case we could create a 'disableBookmarkButton' function and reuse it when we get the result from the datastore and when we get an error from the datastore.

wdyt?