MajorVersion: Major version number (leftmost number) of this browser. For example, for Chrome 5.0.376.86 beta, this field should be set to 5. An asterisk (*) may be used to target any version number, and a question mark (?) may be used to target cases where the version number cannot be identified. For example, Chrome *.* targets any version of Chrome: 1.2, 2.5, 3.5, and so on. Chrome 3.* targets Chrome 3.1, 3.5, but not 4.0. Firefox ?.? targets cases where the ad server knows the browser is Firefox but can't tell which version it is.