I don't know if "content parts" is right but wanted to identify what a web browser (or Firefox) handles. Each "part" is distinct and they're all slightly handled differently in Firefox. There's opportunity to unify how the different parts are handled or managed, and opportunity to specialize? (optimize) the different parts to take full advantage of why they're different in the first place.
Description: html, rss, images
authentication, account, storage of data,
Examples: E*Trade, Google Calendar, Yahoo!Mail, SmugMug, WordPress
Plug-ins (and Helper Applications)
Description: images, video, sounds, other document formats
Plug-in is "in browser" interaction. Helper application is "outside browser" interaction.
Handled by blah, blah
Examples: Adobe Flash Player, Adobe Acrobat, Java Plug-in, RealPlayer, Windows Media Player, Apple QuickTime
Handled by Add-ons Manager
Opportunities to Unify
Opportunities to Optimize