Although your "extension-friendly" launcher is supposed to alter the paths to any extensions to be relative (and seems to work fine), some configuration parameters (for example, "mail.root" as seen with the about.com extension) have the drive letter specified. Obviously, the assigned drive letter may change from computer to computer or depending on how many USB flash drives are connected. At least one extension ("Thunderbird Reset Quote Header" from www.supportware.net/mozilla/) requires you to browse for the text file it will use and then hard codes the drive letter into the configuration (which can be edited with about.com). Consequently, it isn't a relative path, and it doesn't work if the drive letter changes. Under the U3 modifications, is there a work-around or solution to redirect specified drive letters to currently assigned drive letters, or can % be used somehow?