Running from a USB drive - Thunderbird
From MozillaZine Knowledge Base
Can you run Thunderbird from a USB drive (keychain drive)? The short answer for now is no—at least, not easily. For possible workarounds, such as, search the MozillaZine Thunderbird forums for "USB drive" or "USB stick" (both words, without the quote marks). See this thread for one such workaround, in this case a batch file.
Support for USB drives seems to be part of the Thunderbird development vision for 2004, however, so stay tuned.