Please explain the problem in detail. What happens? What is/are the exact error message(s) ?

Try using the 'go back' button on the address bar.

There is no error message, it is just what I said. I would like to return to the addon's original page, from my list of installed addons.

The back button won't help, as that isn't where I just was.

I find it can be hard to search for a specific addon again on the mozilla addons site, so would like to somehow use the addon list to return to the page.

Is what you wanted is to go to the add-ons webpage? There was a Legacy add-on that could do this. I don't know if there is a Quantum version.

What add-ons are you having issues with?

Well, recently "Zoom Image To Fit" is behaving a bit jankily after an update to Firefox, and I wanted to go to the page for that one, but can't find a way.

After using it, you could zoom in/out of the image gradually using the scrollwheel, and pan around by clicking and dragging. Now it's zooming in to a not very useful extreme after moving the wheel one increment, rather than gradually, and won't shrink smaller than the to-fit size rolling the other way.

It's less useful now, and I'd like to ask the developer to update to work around whatever changed, or to file a bug about it if Mozilla busted something, but I cannot find that addon's page.

I could not find that add-on.

Try asking for help in the add-ons forum; https://discourse.mozilla-community.org/c/add-ons