I kept checking back to the reviews in hopes of more info on the installation of "open with", and there it was. I put open_with_windows.py in my Windows\system32......opened a command prompt, which opened in the Windows\system32 folder, and ran the open_with_windows.py install, and that was it for me. I ran test installation in my Browser and Thunderbird, and it showed, "Found version 7.2.3 at C:\​Windows\​System32\​open_with_windows.py." I then edited the order of my four Browsers, with Firefox on top.
Thanks to all the reviews with the help, and thanks to the the Author of this addon!!