selenium - webdriver won't cooperate with firefox -

i have been trying use webdriver run front-end selenium tests, refusing cooperate firefox. try start new firefoxdriver no arguments, , error message.

it says

 selenium.webdriverexception:  failed connect firefoxbinary(/usr/bin/firefox) on port 7055. 

then, says:

 disabling foreign installed add-on fxdriver@googlecode.com in app-profile. 

i have not installed add-ons since starting vm i'm running in. these errors mean?

please check compatibility between firefox , selenium webdriver versions.