By any chance did you use the Reset feature or create a new Firefox profile using the profile manager?

Assuming not...

Does the extension show up on the following tab, enabled or disabled, and what is the version number?

orange Firefox button (or Tools menu) > Add-ons > Extensions category

Note: Disabled extensions appear at the bottom of the list with a grayed background.

Hi there....no the extension did not show up anywhere within Firefox, although I could find a few "reminderfox" mentions on a windows search.

This drove me mad for the morning and half the afternoon (I am one of those people who don't like to be beaten... especially by the computer). So I have now solved my problem.

What I did was to reinstall reminderfox , then, after another search, I just dragged "reminderfox.ics.bak3" (presuming it was the backup) into the icon on the status bar and voila!!! it worked.

Many thanks for picking up on my question