Here is small bookmarklet, which allows to edit the web page for any site (ok, You could save the results on Your local machine only).
javascript:document.body.contentEditable='true'; document.designMode='on'; void 0
The following section in registry should be checked:
HKEY_CLASSES_ROOT\http\shell\open\command
Key: (default)
Most (but not all) browsers check it to determine the current browser.
currentBrowser = RegistryGet("HKEY_CLASSES_ROOT","http\shell\open\command","")
MsgBox( currentBrowser )
Some browsers could create additional section HKEY_CLASSES_ROOT\http\shell\OpenWith\command, which helps to avoid the conflict with IE settings.