This issue only affects some 3rd party extensions in Joomla! versions 3.1.4 and 3.1.5
Fatal error: Class 'JBrowser' not found in path/to/file.php on line XY
After update to Joomla 3.1.4, some some extensions that depend on the native autoloader , with a working code before, may stop working.
While this is not resolved, change the source code from something similar to this
$browser = JBrowser::getInstance(); //...
To this (with legacy way to load classes)
jimport ('joomla.environment.browser'); // Add this linecode $browser = JBrowser::getInstance(); //...