It is not a separate install. It is selected during the install of Studio and Runtime. You can install it manually if you forgot by running "C:\Program Files (x86)\OpenSpan\OpenSpan Studio for Microsoft Visual Studio 2015\OpenSpan.ChromeExtensionInstaller.exe", although the proper way is to select it during install. After installing, launch Chrome and you'll be prompted to enable the extension. After that, you can interrogate.
The Chrome extension is how Runtime interacts with Chrome. The browser extension must be installed and enabled for it to work.
You should not have to change Runtime. It is an option when installing it. You'll also need to provide an instruction to your users on how to enable the extension once installed (extensions cannot be enabled automatically and must be enabled by the end-user).