Only variables should be assigned by reference
Strict Standards: Only variables should be assigned by reference is a common issue regarding the setup of your error reporting in your PHP Setup so is not caused by the extensions of Joomla!
You can try contacting your hosting provider and set the variable
error_reporting = E_ALL & ~E_NOTICE | E_STRICT
error_reporting = E_ALL & ~E_NOTICE & ~E_DEPRECATED
In the Joomla administration navigate to Global Configuration → Server Tab → Find Error Reporting:
Select Option and set the error reporting to None.