These two questions were buried in Comments where they were unlikely to be seen by most readers. For the benefit of everyone who follows this blog, I have copied them here.
1) How can I make Thunderbird my default mail client instead of iMail?
Launch Mail. Select "Preferences..." from the Mail menu. Under the "General" tab you will fins a popup menu "Default email reader:". That is where you can switch to Thunderbird. I don't use Thunderbird, but you may be able to do the exact same thing by selecting the "General" tab in Thunderbird's preferences.
2) I have two NCCMU tabs in the Firefox link line. How can I delete the duplicate one? Draging it into the trash isn't working.
I don't use Firefox anymore, but in Camino (another Mozilla browser) you can select "Show Bookmark manager" from the "Bookmarks" menu.