Selenium-WebDriver 2.53.x not working with Firefox 47 and beyond

The problem

I’m used to running selenium tests against Firefox locally (OS X Yosemite and now MacOS Sierra) both from the command line using RSpec and when using a REPL like IRB or Pry. I don’t use FF often so when I started having issues I couldn’t remember how long it had been since things were working. The problem was pretty obvious. The browser would launch, wouldn’t accept any commands or respond to Selenium and then error out with the message:

Selenium::WebDriver::Error::WebDriverError: unable to obtain stable firefox connection in 60 seconds (127.0.0.1:7055) from /usr/local/rvm/gems/ruby-2.1.2/gems/selenium-webdriver-2.53.0/lib/selenium/webdriver/firefox/launcher.rb:90:in `connect_until_stable’

This occurred for Selenium-WebDriver versions 2.53.0 and 2.53.4. It also seemed to occur for Firefox versions 47, 48, and 49.

The solution

Downgrade to Firefox 45.0 Extended Service Release (ESR).

I’m not the first one to post about the upcoming changes and lack of support for Firefox 47+. I probably deserve the error message for not paying more attention to the upcoming changes and will certainly look forward to implementing the new MarionetteDriver.