Try disabling Tracking Protection for the site(s) as it can be confused with an ad blocker. You are more likely to encounter this with Strict protection, in which case you may want to reduce it to Standard.

I'll try it next time. I forgot to note the URL where it happened :( so hafta wait until stumbling on it again. I'll let you know.

Did you uninstall this extension?

See:

• https://support.mozilla.org/en-US/kb/disable-or-remove-add-ons

Nothing shows there. So maybe it really is uninstalled and your idea above is the way to go.

BTW, what's the difference between an add-on, a plug-in and an extension? Which one of those are ad blockers? How can I see and then delete whichever blocker I still have? Without the icon I can't even disable it for individual sites.

Add-ons is the overall category for extensions, plug-ins and optional themes. Plug-ins and Themes are extremely limited in what they can do, so most of the exciting action is in Extensions.

If you have any extensions installed and enabled, and you have not pinned their button to a visible part of the toolbars, then they should be listed on the drop-down from the Extensions button (puzzle piece button near the menu button). See: Manage your extensions using the extensions button in the toolbar.

If there's nothing there, then you probably do not have any active extensions.

Thanks. It's one of those things that isn't explained anywhere. Now that I think about it, I probably lost the adblocker during an upgrade of Debian. I imported all my old settings from /home, so maybe the icon got copied but not the actual thing -- and the site in question has the other issue mentioned above. Stand by.

I imported all my old settings from /home

Profiles are path-sensitive and can break when moved. Delete extensions.databaseSchema in about:config then restart the browser to fix extensions.

Ok, here was a site that gave the problem:

https://www.baeldung.com/linux/sed-one-command-many-mods

... and:

Delete extensions.databaseSchema in about:config then restart the browser to fix extensions.

... seems to have worked :-)

thanks zeroknight.