Wrong forum.
This forum is for technical support on the Battle.Net Desktop App.
In addition, Blizzard support for Activision games (such as Modern Warfare 3) is limited to issues with installation and upgrades. Any issues that occur once the game is fully installed on your computer (ie, you can click the Play button to launch the game) needs to be referred to Activision Support; see Having Problems with Call of Duty? Read this first! for more info).
There’s a list of known issues on MW3 here:
On that page, there is also a link for a Bug Report form that you can use to report new bugs not on the Known Issues list.