Meh Rated 3 out of 5 stars
[Update: It might just not work when using https://twitter.com] Sometimes it works, sometimes it doesn't. This is the biggest snag for this add-on.
Should work asynchronously to the page load and fill in the gaps, rather than cause the browser to hang.
Needs constant support for more and more tinyurl-esque services and online video providers.
User-preview seemed like a nice option, had it worked. You could simply use the user's page instead of the API and be done with it.
The rest of my review has already been said by others.
Not uninstalling, because it might get updated sometime with bugfixes. Also, when it *does* work, it's a good add-on.