smbMount is an smb:// url scheme handler for Mac OS X.
Since the Finder isn't an smb handler, you can't assign the Finder to open smb links from Firefox or Safari. smbMount will pass those links to the Finder using the "mount volume" Apple Event and they will open as in the "Connect to Server..." menu item.
It will also handle the incorrect but popular SMB:// scheme. smbMount understands embedded usernames and passwords and will give those to the Finder.