I'm experimenting with developing a premium (non-free) version of a popular free Firefox extension that I've written. I'd appreciate any feedback on the methods I'm using to inform users of the free version about the paid version, as well as any general opinions on the feasibility of getting users to pay for browser add-ons, software that is typically 100% free.
Add-on: https://addons.mozilla.org/en-US/firefox/addon/2871/
Landing page: http://www.chrisfinke.com/firstrun/url-fixer.php (shown after the user finishes installing the add-on)