Normally, I dislike "walled garden" approaches.

The problem with browser extensions is that there are too many bad players on the field, preying on the non-technical people. The situation is not as bad as in the IE heydays where I regularly cleaned up 10+ (!) toolbars from customers' computers, but it's still a problem.

And I, unfortunately, don't see any way to avoid a walled garden approach - as long as there is a sideload option like on Android, I'm fine with it.

edit: downvotes? Care to explain how else to solve the bundled crapware toolbar plague?