Are you talking about a Greasemonkey script?
To run a Greasemonkey script on FF you must, of course, install the Greasemonkey plug-in first.
Thank you T.D.M.22 and Huntleigh for responding. Firstly, TDM22 - by putting the name of the script I am having difficulties with as the topic thread name I had rather hoped it was obvious which script I was talking about or is this a generic name for a whole host of scripts?
Huntleigh - I have the Greasemonkey plug-in installed and I believe active but I have only just installed it as it was a pre-requisite to running the GC Google Map enhancement script. If you look at http://www.lildevil.org/greasemonkey/geocaching-google-map-enhancements you will see that the main options are for premium members but here and elsewhere I thought non premium members could get the site name alongside the site icon which is what I wanted, plus I expected to see the premium members filter panel showing even though I cannot make use of them