If you have MTS installed you should be able to click the extension icon and select it from the drop down menu.
Thanks, that's what I thought and I thought I had MTS installed via the TamperMonkey Greasy Fork route, have I made an error?
MTS is its own extension. You don't install it via tampermonkey. There are other scripts that are installed via tampermonkey. Here's the link to the MTS chrome extension https://chrome.google.com/webstore/detail/mturk-suite/iglbakfobmoijpbigmlfklckogbefnlf?hl=en-US