1. I downloaded the firebug xpi file and put it into a temporary
folder.
2. Next I installed firebug by clicking the on the xpi file on the
internet site (not the one on my hard drive)
3. Instead of restarting firefox as suggested I closed firefox
4. Navigate to your profiles folder and then to the extensions folder.
5. create a folder called fir...@software.joehewitt.com
6. Using win zip extract the xpi file in your temporary folder into
the folder created above
7. delete the folder called stagedxpi that should also be in your
extensions folder
8. start firefox firebug should now be available.
Hope this helps someone