Browsers cannot start mstsc.exe directly. This dashboard uses a small custom URL scheme (atc-rdp://host:port) that runs a short PowerShell helper on your PC to launch Remote Desktop—no .rdp file download each time, after you register the handler once.
Set-ExecutionPolicy -Scope CurrentUser RemoteSigned New-Item -Path 'HKCU:\Software\Classes\atc-rdp' -Force | Out-Null New-ItemProperty -Path 'HKCU:\Software\Classes\atc-rdp' -Name '(Default)' -Value 'URL:ATC RDP' -PropertyType String -Force New-ItemProperty -Path 'HKCU:\Software\Classes\atc-rdp' -Name 'URL Protocol' -Value '' -PropertyType String -Force New-Item -Path 'HKCU:\Software\Classes\atc-rdp\shell\open\command' -Force | Out-Null $cmd = 'powershell.exe -NoProfile -ExecutionPolicy Bypass -WindowStyle Hidden -File "C:\Tools\atc-rdp\Open-AtcRdp.ps1" "%1"' New-ItemProperty -Path 'HKCU:\Software\Classes\atc-rdp\shell\open\command' -Name '(Default)' -Value $cmd -PropertyType String -Force