45. A method of supplementing content of a web page retrieved from a first Internet domain with content supplied from a second Internet domain, comprising: at a user computer that has loaded the web page from the first Internet domain for display by a browser, generating a request for a script file, and sending the request over a network from the user computer to a content server in the second Internet domain, wherein the request is generated via browser execution of update handler code associated with the web page, and is generated in response to a determination that the web page includes a link that matches a predefined link signature of a catalog page of an electronic catalog, said request including a product identifier obtained from said link; at the content server, responding to the request by generating a script file that includes content encoded therein, and sending the script file to the user computer, said content being associated with said product; and at the user computer, via browser execution of the update handler code, extracting the content from the script file, and supplementing a visual display of the web page with at least a portion of the content.
45. A method of supplementing content of a web page retrieved from a first Internet domain with content supplied from a second Internet domain, comprising: at a user computer that has loaded the web page from the first Internet domain for display by a browser, generating a request for a script file, and sending the request over a network from the user computer to a content server in the second Internet domain, wherein the request is generated via browser execution of update handler code associated with the web page, and is generated in response to a determination that the web page includes a link that matches a predefined link signature of a catalog page of an electronic catalog, said request including a product identifier obtained from said link; at the content server, responding to the request by generating a script file that includes content encoded therein, and sending the script file to the user computer, said content being associated with said product; and at the user computer, via browser execution of the update handler code, extracting the content from the script file, and supplementing a visual display of the web page with at least a portion of the content. 48. The method of claim 45 , wherein the update handler code generates the request for the script file in response to recognizing that the link is a link to a product detail page of the electronic catalog.