Simple and good Rated 5 out of 5 stars

Has worked for me under every version of Firefox with WinXP. And Firefox doesn't delete the cookies (despite the 27 Sep review).

You can force add-on compatibility by adding a new boolean preference in about:config "extensions.checkCompatibility.9.0" and setting it to false (Where "9.0" is your major Firefox version, put a "b" on the end if you're using a beta).