What can possibly be blocking ads?
From time to time, various sites inform me that I have an ad blocker which is preventing the site from working correctly. I have looked through most if not all of the solutions offered to this problem, but not one appears to be relevant: (1) There is no sign of any ad-blocking add-on or facility either in my Firefox (v46.0.1) toolbars or in my list of installed extensions! (Unless it is Kaspersky's Dangerous Websites Blocker?)
So what can I disable or uninstall? (2) I shall try running Malwarebytes again, but it has never reported any such problem in Firefox before
Alla svar (2)
I see that message a lot. Never had an issue with those sites.
Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac=Options) key, and then starting Firefox.
A small dialog should appear. Click Start In Safe Mode (not Refresh).
Is the problem still there?
Any content blocking, script blocking, or anti-tracking extension could be interpreted by a site as an ad blocker. Sites recognize that the ad didn't load (for some unknown reason) and go from there.
If this happens in a private browsing window, it could be the Tracking Protection feature. If there is a little shield icon to the left of the address, you can use that to temporarily allow the tracking-related content on the page. This article has more information: What happened to Tracking Protection?.