I took a smaller, existing project that runs with the 2012 version and tried to run it with 2013. I have the test list set up to run a login script and then start doing the different tests. The recycle browser checkbox is still set in the 2013 version, but the browser terminates after the login script finshes. It then launches a new browser to do the next test. Since the browser is not already "navigated" to the right site or logged in, all subsequent tests fail. 
(I tried attaching the project, but this small project is still too large to attach.)