Batch - Default Browser?

If you're looking for a Windows .bat solution, this should work on Windows 2000 and later:

reg QUERY HKEY_CLASSES_ROOT\htmlfile\shell\open\command /ve

Result (on my Windows machine)

HKEY_CLASSES_ROOT\htmlfile\shell\open\command
(Default)    REG_SZ    "C:\Program Files (x86)\Internet Explorer\iexplore.exe" -nohome

See the REG.EXE help for more information:

REG /?

Simply use

start www.google.com

See here