Websites tell me to turn the ad blocker off. I don't have an ad blocker. No setting in Firefox says I have one and I don't have any add-on that didn't come with the Linux distro and subsequent updates. But more websites tell me to turn it off and even prevent me from viewing content until I do. And I don't mind the ads. I have two websites of my own with ads served by Google, and I often don't see those ads in Firefox (I have to use Chromium in privacy mode). It turns out the key in Firefox is the shield icon in the Firefox address bar, at the left end, with the tooltip "Tracking attempts blocked". Edit > Preferences > Privacy > Tracking > Use Tracking Protection in Private Windows is the relevant control. Relevant is bug 1206759. I'm using Firefox 50.1.0 on openSuse 13.2 Linux, kept evergreen. Some of my experience above is with prior Firefox versions. I recommend adding information next to the checkbox, specifically, as a line: "This may be perceived by websites as a partial ad blocker, because some ads may track users."

> It turns out the key in Firefox is the shield icon in the Firefox address bar, at the left end, with the tooltip "Tracking attempts blocked". Edit > Preferences > Privacy > Tracking > Use Tracking Protection in Private Windows is the relevant control. Which blocking list do you use?

https://www.mozilla.org/firefox/50.0/tracking-protection/start/ have mentioned the case. I think it is enough, and not too common.

This looks like a misunderstanding. I just would have liked knowing what was causing ad-blocking, not that it couldn't be present. Now that I know, I can set accordingly. But we should be told, because websites are saying something's going on and I didn't think I had an ad blocker. I use the basic protection list, but it doesn't matter which list I use. The browser says that's about tracking, and doesn't mention ad blocking. https://www.mozilla.org/firefox/50.0/tracking-protection/start/ doesn't mention ad blocking at all. It links to https://support.mozilla.org/en-US/kb/tracking-protection-pbm but that only hints at ad blocking, and I think most people won't follow the link. Example of a website complaining tonight: I visited wired.com and selected an article from the home page. I read several screensful of the article at https://www.wired.com/2016/12/white-houses-fix-robots-stealing-jobs-education/ and that's when this popped up: "Here’s The Thing With Ad Blockers"/"We get it: Ads aren’t what you’re here for. But ads help us keep the lights on. So, add us to your ad blocker’s whitelist or pay $1 per week . . . ." This does not tell me what in Firefox is causing the effect of blocking ads. So, before the other day, when I saw a message like this, I didn't know what to change, if I wanted to. Most people, including me, will not assume that an ad is a tracker, so we won't make the connection. The effect is turning up lately on quite a few of the websites I've visited. I don't visit a random sample, so I can't tell how common ad blocking is using the anti-tracking feature, but I expect it to grow if tracking grows among advertisers and if more websites object to blocks.

The purpose of tracking protection is not ad-blocking, it could be a mistake / coincidence if it does, and the issue will be tracked by bug 1206759. So, this could be the misunderstanding or assumption by the site, as well as being a small probability event. Since this is not the intent of the feature and can not be fully anticipated, so its description does not include all possibility of being misinterpreted, including missing elements, failure, can not play and so on.

(In reply to Nick Levinson from comment #3) > But we should be told, because websites are saying > something's going on and I didn't think I had an ad blocker. I think you need to contact websites instead so they provide a less misleading error message. (I have cookies disabled and many websites do not check anymore or display any error message related to cookies. That does not mean that I expect Firefox to explain to me in a more prominent place that disabling cookies might make many websites not function anymore.)

Add the Los Angeles Times' website as saying I have an ad blocker (http://www.latimes.com/business/lazarus/la-fi-lazarus-trump-university-settlement-20161223-story.html#nt=oft12aH-2gp2) ("To read today's stories, please turn off your ad blocker or subscribe") (if you don't confirm the effect with this URL, visit their home page and select a newly published story). The URL's popup window offered me an option to whitelist the site, which in turn gave me instructions for Adblock and for Adblock Plus. Wired treats tracking protection as ad blocking (https://www.wired.com/whitelist-wired/). Both Wired and the L.A. daily newspaper have, I think, large readerships. I have also posted at the Google AdSense forum (https://productforums.google.com/forum/?utm_medium=email&utm_source=footer#!msg/adsense/l6_MLmhKDT0/nvTkGoMqEQAJ), seeking an indirect and incomplete solution (for example, it doesn't address other suppliers of advertising). The websites' staffs may not realize that tracking is built into the ads. They're only publishing the ads, not serving or writing them. Contacting most websites that do this is impractical. I only know about the ones I visit or learn about. Other sites are found by other people, almost none of whom will be reading this thread and thus won't see the advice to contact those websites. Expectations differ between geeks like us and general public users. I had to explain to an upset lay user about how to refresh a page, and she doubtless had the same Firefox documentation that I had. She's a lawyer and can draft a writ but she's not a computer scientist. Even if cookies are disabled and a website says so, you can tell from that message what to do. The tracking/ad-block problem is different because they're apparently unrelated.

Marking P3: This needs product + ux consideration whether or not we would "fix" this.