"Does OpenDNS work correctly with Firefox/AdBlock-Plus?"
Works as expected for me.

OK, I downloaded/installed NetMeter to count bytes coming through my modem..

I ran several web pages through a test with adblock enabled and again with adblock disabled...between each page download I cleared the browser cache and reset the Netzero counters (so I didn't have to do the math-lol) and the results are quite astonishing...with adblock enabled the number of bytes coming through my modem is 25-40% less (depending on amount of ads in the web page) than with adblock disabled..page load times are also 25-40% faster with adblock enabled.

So this proves OpenDNS waits for the browser to request the ads and does not send the ads when adblock is enabled...good show..

I'm sticking with OpenDNS instead of my Wildblue DNS servers..

Rotblitz, you are incorrect. FF has no 'prefetching' features. This is purely an addon feature, usually an addon called SmarterFox does this.

rotblitz, some DNS's use proxy servers to parse the web page that you requested and prefetch ALL the URL's embedded in that page to speed page downloads..it all depends on how the proxy software is written...I noticed that OpenDNS also uses proxy servers for certain functions...that's why I asked.

infinity306 and patchy...I'm using FF 3.5.3 and the tests I just concluded prove that the "prefetch" does not prefetch the ads that are blocked by ABP...

I'll check your concern about the "other DNS traffic" that prefetch might add to my FAP...can you elaborate on this "traffic" with some examples? Thanks..

FYI - You might have to add the network.dns.disablePrefetch setting as the toggle doesn't exist. It's still on though.

It will prefetch any links on the webpage.

Prefetch does not prefetch any link from a web page! It takes a "special" command that's embedded in a web page to trigger a prefetch operation. The technical description of how "Prefetch" works in Firefox is noted below, and an easy way to disable it. Since Google is a big violator of this rule (I use Google a lot) I have chosen to disable Prefetch in my Firefox installation. After you read the following you may also choose to disable it if you are using Firefox..

The technical description of what "Prefetch" does and what triggers it:

In particular, Firefox will, at times, "prefetch" the contents of a web page which it thinks you might want to see soon. If a page is marked as being the "next" page in a series, Firefox, by default, will prefetch that page's contents. (And, yes, for those who have asked for "next" tags for the LWN Weekly Edition, it will happen when we get a chance). When the user hits the link for the next page, it will already be resident in the Firefox cache, and will display more quickly.

The interesting thing is that Firefox can be told explicitly to prefetch pages; all it takes is a tag like:

<link rel="prefetch" href="URL">

Google will, if it decides that you should be feeling lucky, add such a tag to the first in a series of search results, causing that first result to be prefetched.

Google's use of prefetching in this way is unfortunate; it seems certain to lead to trouble for somebody, somewhere down the line. The real problem, however, is with Firefox, which is shipped with prefetching turned on. There is no indication, anywhere in the preference screens, that an option controlling prefetching even exists. Anybody wanting to disable prefetching will have to edit their prefs.js file, or tweak the network.prefetch-next option on the about:config screen. Turning off prefetch in this way will slow down some page loads, but, for many users, the extra delay will be worth it.


A malicious site can already secretly load other sites on your behalf. It's as simple as creating a hidden IFRAME; <link rel="prefetch"> provides no new abilities here. So the use of prefetching by malicious sites is not interesting, and there is no point in Firefox trying to protect you from them.

The only issue is whether friendly sites are using it correctly. So the question is, is Google doing the right thing with its prefetch directives? Their FAQ indicates that they only issue a prefetch when their analysis shows that the vast majority of users go straight to that search result. Whatever bad thing happens when you load that site already happens to 99% of the users with that search term. Furthermore since Google already has some sort of porn detection, that can be applied as a filter too.

Anyway, whether or not Google is doing the right thing, it is not a Firefox issue. Apart from the fact that malicious sites can already get the same effects using hidden IFRAMEs, Firefox has had prefetching for *years* and no real problems have been detected.


Did you know that Firefox has a feature that caches pages that it thinks you are going to click on? This can slow down system performance and add bandwidth usage to your FAP, an important detail if your ISP sets usage limits. Here’s how to disable the Firefox prefetch setting.

1. Type about:config in the address bar and press ENTER.

2. Locate and double-click the entry for
network.prefetch-next

3. Set it to false to disable this feature. Double-clicking on the setting will change it.

DNS prefetching does not download web pages or contents but just resolves the needed info to complete a URL, should the user request it.

DNS Prefetch does not try to resolve relative links, or resolve links whose host is the same as the current page's host, since the current site's DNS record is almost certainly already cached. DNS lookups are performed asynchronously, after the page has loaded, so that your browsing experience is never delayed or interrupted.

Your privacy is safe. While DNS Prefetch does perform a DNS lookup for each different site that exists in a link on your current page, it does not connect to those sites or download any data from them. Unlike page prefetching, the only servers contacted are your computer's DNS servers.

Thanks everyone for your comments..I think we have beat this subject to death and can move on to more exciting things...

BTW...I am totally pleased with my OpenDNS experience so far (3rd day). It does not bog down during peak usage hours like the Wildblue DNS servers do...