unable to obtain stable firefox connection in 60 seconds (not version related?)

I just installed selenium-webdriver (2.45.0) to use with capybara (2.4.0) for feature testing (version from bundle show). I removed the version number from my gemfile for these two to ensure I am getting the latest versions. When I got this error, I searched SO and subsequently downgraded Firefox to version 33.

I have read through all of the "unable to obtain stable firefox connection in 60 seconds" posts on SO and the theme is generally the same - the version of selenium-webdriver does not work with the latest version of Firefox. Unfortunately, I have tried everything suggested and still get the same error.

Is there some other (very basic) thing I may be missing (bearing in mind that I just started with selenium)? Note also that I am using the Cloud9 IDE.

Thanks in advance for your help and suggestions.