Right on the steps of Firefox 8, comes Thunderbird, based on the same underlying Gecko rendering engine, this update comes with a handful of  important enhancements:

• Add-ons installed by third party programs are now disabled by default
• New Search and Find Shortcuts
• Improved accessibility of the attachment list
• Folder switching pane widget removed
• Numerous platform fixes to stability
• Fixed several security issues, including three critical ones

Lightning, the Thunderbird add-on that brings calendar capabilities has also reached 1.0 status, making it the perfect time for trying it.