Extra Thunderbird Format Buttons
After many request by people looking for this functionality (and not finding it in the Text Formatting Toolbar) I have finally written an extension that adds some of the missing buttons to Thunderbird's Compose window. The buttons are a Font size button (in pixels), a strike though, sub script and super script buttons.Download Extension
This will not make a formatting toolbar show in Thunderbird if one is not already there. If you can't see it go to the Tools menu then Account Settings. On the left under your account select Composition & Addressing. Make sure the Compose Messages in HTML format is ticked.