I've got many requests to update Maximize Message Pane (MMP) for Thunderbird3. I didn't know it was used such many users and required even on Thunderbird3. I think Thunderbird3's tab functionality will be an alternative. It is true for some users including me, but now I know there are ones who need MMP since they don't use tabs or don't need the folder pane while seeing the thread pane.
Now you can download the first beta of MMP for Thunderbird3 at my homepage: v1.1.00b1. It has the same functions as ones for Thunderbird2 except for the following:
Jump folder function is removed
Navigation bar is removed
Please report if you find some problems. When new beta is available, the post will be updated. Please keep watching it too.