Well in oder to try and be objective I again d/l Firefox 1.0 and installed it OK.
I decided the one function I cannot live without is mouse gestures so I clicked on the install link on the Optimoz Mouse Gestures 1.0 page. The progress bar zipped across and then a message box appeared telling me the s/w was not installed and to click Options.

There was no where obvious in Options to run this s/w so I went to Extensions where nothing was listed ?? (except some old themes which didn't install either !!).
As I'm obviously too stupid for Firefox I gave up and will continue to use Opera which seems to install any 'themes' and 'extensions' without so much user intervention.