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

Thunderbird, Postbox

Zoom Text Only

Toggle between text and page zoom.

Toggle between text and page zoom.

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

Search Messages

Open Message Search

Open the advanced message search window to find an email.

Compatibility: Thunderbird, Postbox SeaMonkey

Zoom In

Enlarge Text Size

Enlarge the text size on sites that makes the text so small you can't read it.

Compatibility: Pale Moon Thunderbird, Postbox SeaMonkey

Redo

Redo Last Change

Redo the late change.

Compatibility: Pale Moon Thunderbird, Postbox SeaMonkey

Save

Save document as

Save the currently open document, or image to a file.

Saving a page or email for later viewing or to send to a friend is a much needed functionality, so much so that there really should be a toolbar button for it.

Compatibility: Pale Moon Thunderbird, Postbox SeaMonkey

Send Without Save

Send message without saving a copy

Send message with out saving a copy to the sent folder. If you want this as the permanent behaviour, there is an option in account settings under 'Copies & Folders'

Compatibility: Thunderbird, Postbox SeaMonkey

Compact

Compact Folder

Compact all Folders; removes redundant information left from deleted messages.

Compatibility: Thunderbird, Postbox SeaMonkey

Edit as New

Edit Message as New

Edit an email.

Compatibility: Thunderbird, Postbox SeaMonkey

Exit

Exit Application

This button not only closes the current window, but every one that the current application may have open. It is a lot quicker than finding all windows and closing them one at a time.

Finished browsing or reading all your emails, left lots of windows open? Don't want to have to shut them all one at a time? This little button can close them all, with out you having to do it all.

Compatibility: Pale Moon Thunderbird, Postbox SeaMonkey