Original sentence: The pages are either downloaded implicitly into the web browser's own cache as a result of prior online browsing by the user, or explicitly by a browser configured to keep local copies of certain web pages, which are updated when the browser is in the online state, either by checking that the local copies are up-to-date at regular intervals or by checking that the local copies are up-to-date whenever the browser is switched to the on-line
Edited sentence: The pages are either downloaded implicitly into the web browser's own cache as a result of prior online browsing by the user, or explicitly by a browser configured to keep local copies of certain web pages, which are updated when the browser is in the online state, either by checking that the local copies are up-to-date at regular intervals or by checking that the local copies are up-to-date whenever the browser is switched to the on-line state