301 Redirects are permanent redirects intended for use by webmasters to redirect users from one page to another while permanently storing the request so any future requests to that same resource can bypass the server and go directly to the end resource – thus speeding up the browsing experience.
In Firefox and Opera, the cache of 301 redirects is stored separately from the traditional cookie jar. By storing a cookie string in a 301 redirected url, you can effectively keep the same cookies for users even if the cookies are cleared. Visiting this url: https://rehmann.co/projects/301-Redirect-Cookie/ in these two web browsers will give you the same "cached cookie" below, even after clearing your cookies.
Firefox: Ensure Cache and Browsing History are Cleared between sessions to refresh 301 redirect cache
Opera: Ensure Cache is Cleared between sessions to refresh 301 redirect cache
Chrome: Unaffected - Clearing Cookies clears 301 redirect Cache
Safari: Unaffected - "Clear History and Website Data" clears 301 redirect cache
Internet Explorer: Unaffected - "Clearing Cookies" refreshes 301 redirect cache
The current implementation of 301 redirect caching in Firefox and Opera allows for tracking of users who may otherwise believe their sessions cannot be connected to previous web browsing. In Firefox and Opera, web caches must be cleared in order to ensure sessions are disassociated. Firefox users must ensure Cookies and Browsing history are cleared on close. For other browsers, Safari's standard "Clear History and Website Data" function refreshes 301 redirect cache. Additionally, clearing cookies in Internet Explorer and Chrome refreshes 301 redirect cache.