It does exactly as claimed, and no more: the web-site on your active tab will treat you as if you had just connected to it for the first time, the other tabs you keep open in Firefox will not be affected. I find this very useful in many circumstances.

Howdy Partner.

This is the only extension that actually clears the cache and the cookies for the domain your in regardless of other tabs. Even the other extensions explicitly saying hard refresh do not hard refresh. Momentarily the other tabs cannot write to the cache.
I mean , wow, It just works....The Mind Boggles! Amazing !!