Include a PHP resource within a Plugin
The first one example should work as long as the last BrowserDetection segment maps to the actual BrowserDetection.php file on the file system.


  Fatal error: Class 'Craft\BrowserDetection' not found in /Volumes/Mark Notton/Clients/The STC/Website/craft/plugins/myPlugin/MyPlugin.php on line 33


You'd still even get that error on the first one because the BrowserDetection class is in PHP's global namespace.

You need to do:

$browser = new \BrowserDetection();