These are a ready make selection of some of the most popular buttons from the Custom Toolbar Button Maker
Thunderbird, Postbox
Toggle Toolbar

Toggle the main toolbar from showing to hidden. Don't place it on the main toolbar, it is disabled then and will not work.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Toolbar Display

Set the toolbar icon size as either large or small, and the button display mode between icons, icons and text, or text only.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Toolbars

Show and hide toolbars quickly and easily.
Toolbars use up valuable screen real estate, removing them frees this up to show more web page or email depending on what your doing.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Unread Threads

View threads that you have not read yet.
Compatibility:
Thunderbird, Postbox
SeaMonkey
Update

Check for updates to the currently open application.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
View Menu

Show the view menu.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Watched Threads with Unread

View watched threads that have unread messages in them.
Compatibility:
Thunderbird, Postbox
SeaMonkey