To the browser, it doesn't matter. For matter of semantics, it only matters if you're prototyping a function or using the function statement.
function stuff(stuff) {
alert(stuff);
} //don't need a semicolon
Object.prototype.stuff = function(stuff) {
alert(stuff);
}; //need a semicolon
var stuff = function(stuff) {
alert(stuff);
}; //need a semicolon