For sites that has x free articles/month, I just discovered Private Tab[1] which makes it easy to turn an existing tab private or force a bookmark to always open in a private tab.
Self-Destructing cookies extension also keeps the read count at 0 after you close the tab. As an added bonus the extension should also help prevent you from being tracked across the web by various advertising/state agencies.
[1] https://addons.mozilla.org/en-us/firefox/addon/private-tab/