Browser is the term used for programs that you access the web with. The WM script is designed to run in the Firefox browser. Use the most recent standard release of FF unless otherwise noted on the Known Issues page.
This script does not work with Google Chrome because that browser does not allow the control of windows by another window, or script running therein. Due to this, Google Chrome users will not be able to get the Sidekick scripts to communicate with the main WM body. For many posts, no bonus collection will occur. Recently Users have been using TamperMonkey to get WM to work on Google Chrome with good success rates.
Since I personally run only Firefox, and only occasionally switch to Internet Explorer for emergencies, I code specifically for Firefox only. If you want to try to run this script in other browsers, you are on your own.