You go to chrome://extensions/ There you enable developer mode in the top right corner. You extract the zip with the 2 files somewhere you can find it. After that you click in the top left a button called "Load unpacked" and select the folder. And it should be added and working.
Go to about:debugging#/runtime/this-firefox click on "Load temporary Add-on..." Select the manifest file from the extracted folder. (You need to do this every time you boot up firefox unless you know what you are doing.)