I seem to remember windows' start command is a console app, so if you're running in a GUI it has to spawn a console to run start. start itself then spawns an external program and quits, hence the flash of a console window.

If you can always be sure that the browser will be IE, then you can use:

system( "iexplore.exe http://myurl.com" );
[download]

Failing that, you should be able to lookup in the registry the default association of .html files. I think it's this:

[HKEY_CLASSES_ROOT\htmlfile\shell\open\command]
[download]

Otherwise, have a play with Regmon and see what keys are being queried when the default browser is started. You can then query the same keys in Perl and invoke that browser directly.

Update: Ah, jasonk has a much more simpler solution. But it's much more fun to have an purely Perl approach ;)