Types of Updates
There are several ways we update users between different versions of Firefox, and several ways we offer those updates. The terms below are meant to be interpreted from the perspective of the end user with default prefs.
The distinguishing feature of automatic updates is that they will be, by default, downloaded and applied automatically once they become available. A dialog will be presented to the user notifying them that the update has been downloaded and is ready for install.
Automatic Updates are typically done for security and maintenance releases, i.e a minor version change only, e.g. 3.5.7 → 3.5.8
An advertised update is one where the user is presented with a dialog asking them if they would like to download and install the update.
Advertised updates are typically done for major product changes, e.g. 3.5.7 → 3.6.
Content (webpage on mozilla.com) that appears in the advertised update dialog.
A manual update is one where the user must go to the Help menu and select "Check for Updates" to discover and apply the update.
Both of the other two types of updates are also available via this mechanism.
These terms are confusing, so please don't use them any more.