pretty simple when you get a hang of it
Invoke-WebRequest "https://download.mozilla.org/?product=firefox-latest&os=win64&lang=en-US" -OutFile FirefoxSetup64.exe

should help you install firefox without messing with the lame IE Protected Mode

more here
http://superuser.com/questions/362152/native-alternative-to-wget-in-windows-powershell
http://stackoverflow.com/questions/4619088/windows-batch-file-file-download-from-a-url