The Gmail Button add-on is a button that can be located anywhere in the toolbar, when clicked checks for a gmail homepage. If there is an open gmail page, it does nothing.If there is no open gmail homepage it opens a gmail page.
How to Install in Thunderbird:
1. Right-click the link below and choose "Save Link As..." to download and save the file to your hard disk.
2. In Mozilla Thunderbird, open Add-ons from the Tools menu.
3. Click the Install button, and locate/select the file you downloaded and click "OK".
· Mozilla Thunderbird