Adding custom controls to Thunderbird (Extension)

I need to add a button next to From tag in the messeg开发者_如何学JAVAe header.

Anyone knows how to do this?

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Add an overlay to content/messenger/msgHdrViewOverlay.xul. In it,

• Define a button element as a child of <row id="expandedfromRow">.
• If you probably wanted to have a new button alongside the reply, reply all, forward buttons, you should add a new toolbarbutton element as a child to <toolbarpalette id="header-view-toolbar-palette">.

If these steps are not clear to you, let me know, I will elaborate. Thanks.

P.S.: These steps are for Thunderbird 3+.