Assuming this on chrome.manifest:
overlay chrome://messenger/content/mailWindowOverlay.xul chrome://myext/content/thunderbird-overlay.xul
Add the next in thunderbird-overlay.xul.
For Thunderbird 2
<?xml version="1.0"?>
<overlay id="sample"
xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
<menupopup id="messagePaneContext">
<menuitem
id="my_option"
label="My option concise and cool label"
oncommand="alert('Hi')"/>
</menupopup>
</overlay>
For Thunderbird 3
<?xml version="1.0"?> <overlay id="sample" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"><popup id="mailContext">
<menuitem id="my_option" label="My option concise and cool label" oncommand="alert('Hi')"/>
</popup> </overlay>
For Thunderbird 2 and 3 in the same XPI
If our extension needs to support Thunderbird 2 and 3 we need to make custom overlays for each version. This can be reached by adding these lines to the chrome.manifest
file:
overlay chrome://messenger/content/mailWindowOverlay
.xul chrome://myaddon/content/tbOverlay-tb2.xul appversion<3.0 overlay chrome://messenger/content/mailWindowOverlay
.xul chrome://myaddon/content/tbOverlay-tb3.xul appversion=>3.0
Than we need two overlay XUL files with content from examples above.
Note: If our extension supports more Mozilla applications (for example Mozilla Firefox and Mozilla Thunderbird) we need also specify
application
flag. For more details see Chrome Registration.