I think this can go back to simply being 

```
var isChrome = !!window.chrome;
var isFirefox = typeof InstallTrigger !== 'undefined';   // Firefox 1.0

if (!(isChrome || isFirefox)) {
    alert(OpenLayers.i18n('unsupportedWarningMessage'));
}
```

But I would think extracting the chrome and firefox checks into functions would be neater;

```
isChrome: function() {
    return !!window.chrome;
},

isFirefox: function() { 
    return (typeof InstallTrigger !== 'undefined');
},

browserCheck: function() {
    if (!(isChrome() || isFirefox())) {
        alert(OpenLayers.i18n('unsupportedWarningMessage'));
    }
}
```