I am confirming this bug. I have Win 7 64 bit, running Tor browser 7.5 (latest stable release) with MBARW 1.1.129. I tried using 'new identity' in Tor and it failed in exactly the same way. Then I disabled MBARW and 'New Identity" worked. Then I reenabled MBARW and 'New Identity' failed again. Not only that, MBARW also Tor browser to be unable to change user settings in general: Tor forgets after closing the window if I want to use a Bridge or just connect, what security setting I last had, and if I disabled the "Do you want to close 5 tabs" popup. I confirmed these too in the above manner.