Application Menu: With the release of Thunderbird 17 there is an application menu entry on the Toolbar that is shown below. Clicking the application menu will provide access to most of Thunderbirds menu options. Most support articles on the web however do not refer to this application men, but to the Full menu bar
Full Menu bar: Pressing Alt will show it long enough to enter some key strokes. Pressing F10 will make it visible for a longer time..
Toolbar: Once you have the menu bar visible, selecting the view menu item and then toolbars will show the list of toolbars you can have visible.
The Mail Toolbar is the main toolbar with Icons on it.
Menu bar is the application menu. This can be made visible either by holding the ALT key or pressing F10
Status bar is at the bottom of the screen
Quick filter bar has the same effect as clicking the magnifying glass icon on the toolbar or Tab bar (Up to V11)
If you are in the compose window the options are shown above. It is only from the composition window (click write or reply etc). that the toolbars shown in that windows can be set.
Menu bar is the menu for the composition window only. This can be made visible either by holding the ALT key or pressing F10
Composition Toolbar is the main window toolbar with send on it
Formatting bar is the bar that has formatting information on it like font name and size
Status bar is the footer at the bottom of the screen. Used for feedback and by add-ons. In my case I can access a translation add-on there.
Tabs and toolbars:
From Thunderbird version 11 toolbars will be under the tabs, and the toolbar that appears will be dependent on the 'context' of the tab. What this means is that the mail toolbar will not be visible unless the tab is a mail tab. Lightning will have a Calendar toolbar, and some other tabs will have no toolbar at all. This change is I am told in preparation for bringing compose in a tab and address book in a tab to fruition. For those that are interested these Thunderbird bugs refer to the change and the request I made to provide an option to opt out of the change.
In response to customer complaints about the change, the Rise of the Tools add-on was born to reverse the layout changes and put the toolbar and menu back on top.