These are a ready make selection of some of the most popular buttons from the Custom Toolbar Button Maker
Thunderbird, Postbox
Undo
Undo last change/action.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Toggle Proxy
Toggles the Proxy between on and off for quick changing of networks.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Options Menu
Show the options menu in the compose mail window.
Compatibility:
Thunderbird, Postbox
SeaMonkey
Print Preview
Open the Print Preview to view a page before printing it.
Paper costs money (and trees) so it is worth checking what the page looks like before you print it. Though it has always amazed me just how much the button gets downloaded.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Save Attachments
Save Attachments from an message.
Compatibility:
Thunderbird, Postbox
SeaMonkey
Format
Show the Format Menu
Compatibility:
Thunderbird, Postbox
SeaMonkey
Free Memory
Free unused memory that Firefox is currently using.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Options
Opens the Options window so you can change settings easily.
Firefox, Thunderbird and Sunbird all have a huge number of settings. Often you will find a need to change one. About to visit your banking site, so you want pop ups enabled, or what ever your current need might be. The button brings the option window to you quicker.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Run Application
Runs an external application
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey
Switch Profile...
Switch the Profile that you are currently using.
Compatibility:
Pale Moon
Thunderbird, Postbox
SeaMonkey