Firefox, Chrome and other browsers offer option on the context menu to open link in incognito mode, how about opening a page in Private window? That option is not provided in browsers by default, but there is an extension available for Firefox, created by Chris Peterson, technical program manager at Mozilla.
Open Page in Private Window is that extension (in fact, it is an webextension), which after installing, adds Ghost icon to the toolbar and also offers context menu option. You can use either to open a copy of the current page in a private window. The developer hopes his extension, which doesn’t close original tab or clears browsing history, will be useful for ‘reading articles on websites that limit the number of articles you can read per month’.