The Gecko web driver version 0.18 contains a bug where the Firefox browser will not load a local file when navigating the file path, this causes the Firefox browser to hang indefinitely. To resolve the issue it is recommended that you upgrade to the latest version of Firefox (56 ) and to ensure that you are using at least Silk Test 18.0 HF2  as this contains a fix for the issue.

If you are unable to upgrade the version of Firefox and Silk Test, please see the steps below on how to revert to an earlier version of the Gecko WebDriver to be used by Silk Test:

1) Close the Open Agent

2) Close Silk Test

3) Download the Gecko Driver version 0.16.1 from https://github.com/mozilla/geckodriver/releases

4) Navigate to the Silk Test installation directory\ng\WebDrivers\Windows\Gecko

5) Rename the folder '0.18.0' to 'Old_0.18.0'

6) Create a folder '0.16.1' and copy the contents of the download to this folder

7) Start Silk Test and run a test

Silk Test will now use the older 0.16.1 gecko driver for Firefox automation where the bug does not exist.