Hello JillD-MN
I am very sorry for the inconveniences.
Sadly, starting a few years back, Mozilla disabled direct access to WIndows API, making it impossible to directly put a windows on top. Instead, they provided this mechanism of external apps that extension devs could use.
But, you don't have to download already built app, you can download its source code and build it instead. In this way you will be able to control what the code does yourself.
I hope this helps

Please feel free to ask more questions if needed
Best regards,
Vasyl Maherka