Can't open owasp-mantra, firefox already opened

I'm learning Kali Linux, tried to boot Mantra, but I always got the error msg like this:

'Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.'

I tried killall firefox, killall firefox-bin, restart my system, install xterm, but they didn't work...

I got these as well:

wasp-mantra-ff
firefoxportable:Debug/Info: 0=./OWASP Mantra
firefoxportable:Debug/Info: dir=/usr/share/owasp-mantra-ff
firefoxportable:Debug/Info: Current Dir=/usr/share/owasp-mantra-ff/Mantra

(process:1816): GLib-CRITICAL **: 14:50:06.375: g_slice_set_config: assertion 'sys_page_size == 0' failed
Welcome to the Linux version of firefox 18.0 in portable mode. Feedback is NOT disabled.
firefoxportable:Debug/Info: Profile Directory already exists!
Warning: Tried to connect to session manager, Authentication Rejected, reason : None of the authentication protocols specified are supported and host-based authentication failed
firefoxportable:Debug/Info: firefox is now closed.
./OWASP Mantra: 51: yaf-splash: not found
firefoxportable:Debug/Info: firefoxportable is now closed.

Can anyone help me? THX!!!