Bon Echo Beta 2 Portable remapped my "My Documents" folder. I think.
Like it says. I tried importing preferences into Tab Mix Plus, but when I clicked My Documents in the open dialog it showed a blank space. I went to Windows Explorer and saw that when I clicked My Documents I was redirected into Firefox Portable/Data/userprofile. I use the FirefoxPortable.ini file to map userprofile to that folder, as specified in the Firefox Portable support page. I'm not sure what exactly caused this, but the only thing I was doing at the time was installing extensions and configuring a newly downloaded Beta 2 Portable.