Ubuntu – All browsers with one icon in the launcher!

I'm trying to create my first launcher for Unity that works like this:

when I use the left-click, it opens the browser set as default on the system
when I use the right-click it opens 3 shortcuts related with the other browsers of the system.

But I'm having this problem: for each shortcut, unity is duplicating the icon on the launcher. I wanna all the browsers set on the same icon.
Is that possible?

Here is the code:

[Desktop Entry]
Version=1.0
Name=Brox
Comment=Navegue pela Internet
GenericName=Brox
Exec=sensible-browser %u
Terminal=false
Type=Application
Icon=/usr/share/icons/Faenza/apps/scalable/brox.png
Categories=Network;WebBrowser;
MimeType=text/html;text/xml;application/xhtml+xml;application/xml;application/vnd.mozilla.xul+xml;application/rss+xml;application/rdf+xml;image/gif;image/jpeg;image/png;x-scheme-handler/http;x-scheme-handler/https;x-scheme-handler/ftp;x-scheme-handler/chrome;

X-Ayatana-Desktop-Shortcuts=Google Chrome;Firefox;Opera;

[Google Chrome Shortcut Group]
Name=Google Chrome
Exec=/opt/google/chrome/google-chrome %U
OnlyShowIn=Unity

[Firefox Shortcut Group]
Name=Firefox
Exec=firefox %u
OnlyShowIn=Unity

[Opera Shortcut Group]
Name=Opera
Exec=/usr/bin/opera %U
OnlyShowIn=Unity

Thanks in advance