A process is directed to the generation and processing of browser virtual machines. A network computing provider determines browser settings and other optimizations for improved performance when a browser is processing a specific type of Web page or other network resource. The network computing provider customizes a browser with the settings and optimizations, and generates a virtual machine image of the customized browser. The image is deployed to any number of servers processing network resource requests from client computing devices. In response to receiving a request for a Web page or other network resource with a corresponding customized browser, the network computing provider routes the request to a server with an image or active instance of the customized browser.