Override client version properties are used to selectively replace default client version properties of a web browser to obtain versions of web resources that are operational on the web browser. A client operating the web browser issues a request for content through a proxy server. Using an index, the proxy server determines whether the content is to be requested using an override client version property set. If so, the override client version property set is used to request the content form the web server and causes the web server to respond with content that has been designed or optimized for a web server other than the one operating on the client. Accordingly, the client can obtain fully functional and operational versions of the web resources using client version properties that are selected based on the capabilities of the web browser and the functionality available in different versions of individual web resources.