Usually it would be among your extensions:

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

If it is disabled, it will be in a grayed out area at the bottom of the list.

If the HP software did not add the extension to Firefox by dropping it into a shared extensions folder or creating an entry in the registry, perhaps there is a feature in the software to prompt it to do that? Or if it is nondestructive, you could try reinstalling it.

Thanks for responding. While the laptop is an HP, the desktop computer is not an HP, but a Dell.

I did check the "extensions" sub-folder, but the extension was not shown.

When I tried to search within Firefox's inventory for all available plug-in, I could not locate any "Post-it Digital Notes 5.3.0.0002" among those listed. Thanks.

3M charges for this program, so maybe it is free from HP and not Dell?

I found the trial download page here: Post-it® Digital Notes

If you prefer a free note-taking program or add-on, it appears you have plenty of choices, but I haven't tried any of them myself.

Thanks for response. I have used the 3M software for some time now; and I wanted to keep that software on both the desktop and laptop. When I bought downloaded and installed the software on a new HP laptop, Firefox responded with a warning that an entity wanted to install the extension, etc. I then researched the extension name and searched for it using the Dell desktop but was unsuccessful.

I appreciate your help, but I'll stick with Post-It Digital Notes. Thanks.

Thank you for the clarification. If you aren't able to get the extension installed on both computers, using that same technique, perhaps 3M can explain why it is missing.

Thanks for the suggestion. Don't know why I hadn't thought about contacting 3M; and I wll.