Changes

A feature is a "shippable unit", a well-scoped and atomic piece of work that improves a part of Firefox. This is a smaller unit than what we normally think of as featuresa feature, but with conceptually larger than a single typical bugfix.

Something like "Create a Home Tab as a Permanent App Tab" is a feature under this definition, whereas "App Tabs" is too large to be well-scoped. "App tab rendering glitch on OS X" is too small to be worth feature tracking, and as it is really just represents single bugfixing a flaw rather than adding to the product or changing how something behaves.