You need to enter into a different realm, because as far as I know, what you want is not possible, at least in the way you are probably thinking.
You want web browsers to show an embedded C++ game. Well, browsers don't care if it is a game, a video player, or anything else. Browsers support specific standards. If you want to go cross-platform, you'll require Java or something else. Browsers can embed Java applets. If you want to maintain the core of the game in C++, then you have to write it in a way that Java can access it. Java can access COM. C++ can do COM. Program your game as a COM component.
If you are thinking Windows, then COM itself is good enough. Actually, ActiveX. There is a very thin and obscure line between the terms "COM component" and "ActiveX component". If you target Windows, you can do it entirely in C++ by making the game an ActiveX component.
There might be other ways to do it cross-platform or even Windows-specific. Let's see what others have to say about this.
If you look at big games ie World of Warcraft, MapleStory... none of them are actually run in your web browser. Such a compatability would be very exciting, but its just something that can't be done without getting into a cross-platform mess. If you really want to do that... Look at Java. I made this game entirely in java (its only in Beta)... its currently host it on my website: