There is no built-in support for Selenium WebDriver from Firefox 47+, you need GeckoDriver. Installation of GeckoDriver is the same as ChromeDriver. We received several enquires on TestWise no longer works with Firefox 47+. The solution is to download the working version of GeckoDriver and put it in the PATH.
GeckoDriver is still in beta, and we had issues with one version works on Firefox 47 but not 48. To avoid the hassles for TestWiser Community Edition users, We switched the default (and only) browser to Chrome. This makes sense too, as Chrome is the most used browser and the convenience of built-in support for Firefox no longer exists.