Put the following batch file somewhere and create a shortcut to it in %USERPROFILE%\SendTo
for /d %%X in (%*) do (
start "" "%%~X"
Select files, (any files), right-click -> Send To -> Open Files
The selected files will open in their default program.
NOTE: CLI windows will open, they may close depending on the application that's run. If you don't want CLI windows opening then download cmdow
and change:start "" "%%~X"
to:<path to>cmdow.exe /HID /RUN "%%~X"
ALSO NOTE: Whether or not URLs each open in their own tab depends on whether you have Firefox set for Single Window Mode.