Firefox Plugin idea
I would call this the "Productivity Plugin". And its rather simple.
A plugin that restricts to only one instance of browser (maybe in kiosk mode), and limits the user to open up only 5 tabs simultaneously.
Consider how much time and resource we waste by opening so many browser windows and tabs, which we have even no time to look at. And how much time and resource this simple plugin would save. This is something the machine should force us to do.
Add a timer to it to measure how much time is spent browsing the web. And a "Getting Thing Done" style todo-list tracking tool (http://trimpath.com/project/wiki/NextAction)
Microsoft already has done this in their new version of Windows.... the one that only lets you run two or three apps and no more. They say it is to make the OS more affordable... perhaps they are also making it more efficient too.