Ok, assuming that most major web surfers are at least somewhat computer literate and have at least heard of Firefox why wouldn't they switch? Other then web developers needing to have a copy of IE to test code why would anyone use IE when Chrome, Firefox, Safari, etc are all technologically superior and have more plugins?
Users need compelling reason to switch. Technological superiority doesnt sell itself, there needs to be a reason to move, a reason to download something else and to relearn a new interface and to shuffle bookmarks and customizations into a new system.
Systems like Extensions and Jetpack exist as precursors to incentives: they themselves offer nothing of value to end users, and only serve as progenitors for incentives to be created.
These incentives are still highly detached: a user isnt saying, I'm switching to Firefox so I can use Vimperator, they're saying, I'm switching to firefox so I can go find and install the Vimperator plugin. And typically its not one particular plugin, its the accrued group of plugins each user build that makes them dedicated to Firefox, there are very few killer features. To answer your question, the immediate value proposition of switching to Firefox is minimal: it and IE are both web browsers, and they generally render most sites with parity.
Jetpack and its father-in-kind Chrome Extensions in particular are trying to close the loop some, and at least increase accessibility of enhancements.