Instead of this: user_pref("browser.cache.directory", "C:\\Documents and Settings\\blah\\Application Data\\Mozilla\\Profiles\\blah\\blah.slt\\Cache"); user_pref("mail.directory", "C:\\Documents and Settings\\blah\\Application Data\\Mozilla\\Profiles\\blah\\blah.slt\\Mail"); Use this: user_pref("browser.cache.directory", "Cache"); user_pref("mail.directory", "Mail"); I can think of 3 reasons to do that: 1. Being able to move profile folder and still have working preferences 2. Using the same profile directory from another OS. For example mounting a FAT32 drive under Linux and symlinking ~/.mozilla/ to the Windows Mozilla profile directory, instead of creating a new profile under Linux. 3. Migrating profile files on a new/another OS installation. When new profile gets created, *.slt folder gets a different name, and even if you place all your files inside of it, the prefs paths will still be broken. Ofcoarse in Windows, if say Cache folder is located on a a drive different from profile drive, the path will have to stay full. Bug 157662 raises similar issues with profile directory path being relative. But even if that bug gets implemented, the prefs will still be broken.

*** This bug has been marked as a duplicate of 137006 ***

v dup