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

Thunderbird, Postbox

Find Previous

Find Previous Match

Find the previous bit of text that matches your search.

Compatibility: Pale Moon Thunderbird, Postbox SeaMonkey

Get Inbox

Change Focused Folder to the Inbox

Change the currently selected folder to your Inbox.

Compatibility: Thunderbird, Postbox SeaMonkey

Help

Open help documentation

Open the application help documentation.

Compatibility: Pale Moon Thunderbird, Postbox SeaMonkey

Help

Open Help Menu

Show the Help Menu

Compatibility: Pale Moon Thunderbird, Postbox SeaMonkey

HTML Mode

Set if Message is shown as HTML or Plain Text

Set if the message is displayed as HTML, sanitized HTML (all the possible nasties removed) or as plain text.

Compatibility: Thunderbird, Postbox SeaMonkey

Ignored Threads

View Ignored Threads

View all the threads in the current folder that are set as ignored.

Compatibility: Thunderbird, Postbox SeaMonkey

Insert

Show Insert Menu

Show Insert Menu

Compatibility: Thunderbird, Postbox SeaMonkey

Languages

Open Language Manager

Open the Language Manager to enable or disable or do any other needed tasks to any of your language packs.

Compatibility: Pale Moon Thunderbird, Postbox SeaMonkey

Message

Show the Message Menu

Show the Message Menu

Compatibility: Thunderbird, Postbox SeaMonkey

Message Pane

Toggle Message Pane

Show/Hide the Message Pane.

Compatibility: Thunderbird, Postbox SeaMonkey