Using this guide
This page lists the current (as of Dec. 01, 2010) list of Mozilla interfaces as listed on the XPCom interface Reference Page Where that page lists items by alphabetical sorting, this page attempts to group them by function. Grouping and category names were made by somewhat arbitrary decision by the author. (I'm fully aware that this will be a great point of discussion and probably will end in tears, but since I'm the first person to apparently take a swing at this, I get first dibs.)
The primary sections consist of:
This section contains elements associated with the view pane or the content of the "browser window" proper. It is wrapped by System, but displayed for convenience.
This section contains Data wrappers and core object definitions.
This section contains APIs for secure channel communications
This section contains Application level interfaces including calls to external support elements (such as device calls). This is the root element and may contain some functions defined in other groups.
This section contains elements specific to a given user's data storage.