Enumeration of Installed Browsers (and versions)

In a Delphi app I would like to know, on  any given machine, which browsers (IE, Opera, Firefox, Mozilla, Netscape) are installed (preferably also which versions), to display that info to the user, and then to display a page in the selected browser.

For IE this is reasonably well trodden ground.

check for IE and version
http://www.swissdelphicenter.ch/torry/showcode.php?id=413
http://www.swissdelphicenter.ch/torry/showcode.php?id=1252

obtaining the path to the default webbrowser
http://www.swissdelphicenter.ch/torry/showcode.php?id=120
looks at
HKEY_CLASSES_ROOT\htmlfile\shell\open\command

but that tells me nothing about the other installed browsers.

Any good ideas ??  Maybe someone has a listing somewhere of where the browsers are typically installed ? But that is not bulletproof, there could be custom installations. Search the hard disk for opera.exe, firefox.exe etc? .. apart from being kludgy and time-consuming that approach is not bulletproof either, simply finding an exe is not proof that it has been or is currently installed.

thanks