The performance concern can be addressed by monitoring it and informing the user when extensions slow down page loads. The security concern is difficult to sol

The performance concern can be addressed by monitoring it and informing the user when extensions slow down page loads. The security concern is difficult to solve (more fine-grained permissions might help), but also seems a bit disingenuous since extensions can also inject code into the HTML of all sites and already syphon off a lot of data if they want to. Sure, it's a sharp knife, but some tough issues require sharp tools.