Thank you for your interest in Test Studio.
Please note that the current latest Firefox version is 57 which is quite different designed in comparison to the old versions. This includes major changes in the extensions compatible with the new Firefox. Therefore we had to rework and adjust our approach towards that browser. Please find some additional information here
in regards the Firefox extensions.
As of our R3 release (v.2017.3.1010) we introduced a single extension for recording and execution compatible with Firefox after v.56. Thus if having any old versions of the browser you have to downgrade Test Studio as well so it is compatible. Any version before 2017.2 (including 2017.2.824) will install the previous two extensions and could be used to automate testing against Firefox.Though you should be informed we could not commit with possible fixes if you encounter any issue.
I hope this information will be helpful to you.