vidalia yellow, tor connected, firefox not launched

i get this behaviour maybe 1 in 10 times.

1. i type start-tor-browser
2. vidalia comes up and completes almost everything (log attached)
3. no sign of firefox.

i can work around it every time by hitting Stop Tor in vidalia, then Start Tor.

is there a way to get more debugging info out of TBB ?

lubuntu 12.04 x64
tor-browser-gnu-linux-x86_64-2.2.39-5-dev-en-US.tar.gz (but it has happened with all previous tbb iirc)

Trac:
Username: keb