U3 - Thunderbird
From MozillaZine Knowledge Base
Mozilla Thunderbird for U3 is a version of Mozilla Thunderbird modified to run on U3 smart drives (USB drives). A U3 smart drive supports Vista (requires U3 Launchpad version 1.4 or higher), XP, and Win2k SP4. It uses AutoPlay to run the U3 launchpad, which is used to launch U3 applications. Mozilla Thunderbird for U3 is a copy of Mozilla Thunderbird plus a launcher. The reason for the launcher is to let you use a profile stored on the USB drive, without having to install/configure anything on the PC.
It is recommended that you switch to Portable Thunderbird.
The last version offered is the badly outdated 22.214.171.124 (updated Sep. 17, 2007). It is not clear who ported it. Version 126.96.36.199 was the last version ported by John Haller, the same person who created "Mozilla Thunderbird, Portable Edition" (aka Portable Thunderbird). He has stated:
"U3 will be phased out next year. Sandisk and Microsoft are working on yet another new portable platform. It will be tied to hardware and only work with XP and Vista. Sandisk has indicated that U3 apps and hardware will not be compatible with the new platform. So, essentially, current U3 hardware and software is a dead end."
This article states: "Major suppliers have already dropped the U3 platform because of high royalty fees (around 5%) to bundle less expensive software which does the same thing. As these suppliers, like Kingston and Memorex, begin to choose the alternate like Migo Software, a heated war could surface between flash drive manufacturers."
Microsoft and U3 have also announced a partnership to create StartKey. The biggest difference is that it is intended as a key component in logging in and booting up Windows. It supposedly "will allow users to bring along their wallpaper, icons, desktop layout, contact lists and key applications to any other Windows system."
If you want to use Mozilla Thunderbird for U3 see this post for how to move your profile to it.
The U3 community forum and the SanDisk Cruzers with U3 forum have some threads about Mozilla Thunderbird for U3 but the best support appears to be the the U3 forums on the Portable Apps web site. They're no longer listed on the web sites main page but are still accessible.