I believe that extensions like this have a significant role to play. Bugzilla’s Tech Evangelism project is overflowing with badly designed sites that through ignorance or choice refuse to work with standards compliant browsers, many of which have available patches just waiting to be implemented. Per-site extensions at least allow users to choose to fix the problem locally and route around the damage—and their use should send a powerful message to the sites in question.
This kind of extension also introduces some interesting questions. How will site owners react to their users tweaking their websites in this way? Is it ethical to modify a site without the user’s permission to improve functionality? What about to block irritating ads?
Pop-up blockers have only scratched the surface. Let’s see some innovation.