Mozilla Blocks McAfee ScriptScan Add-on

Martin Brinkmann
Oct 5, 2011
Updated • Mar 9, 2015
Firefox, Firefox add-ons

Mozilla has made the decision to add McAfee's ScriptScan add-on for the Firefox web browser to the browser's Blocklist. The Blocklist lists add-ons and plugins that are known to "cause serious security, stability, or performance issues with Firefox".

When users try to open the McAfee ScriptScan or McAfee SiteAdvisor page on the official Mozilla Add-on repository, they are redirected to the add-on's Blocklist entry.

The reason for blocking the add-on is a high volume of crashes according to that page. Affected by the block are all ScriptScan versions 14.4.0 and below for Firefox and Seamonkey, and users of McAfee SiteAdvisor.

Firefox users who run one of the blocked add-ons in the browser will see the following message in the web browser: Firefox has determined that the following add-ons are known to cause stability or security problems

A click on Restart disables the listed add-ons completely. Users who try to install the add-on see a similar message: The add-on name has a high risk of causing stability or security problems and can't be installed.

The initial bug report requested to add McAfee ScriptScan and McAfee SiteAdvisor add-ons to the blocklist. It also mentions that both add-ons have caused more than 10,000 crashes in a one week period for Firefox 6.0.2 and Firefox 7 users.

Even worse, if you follow the initial bug reports you will find a comment by Robert Kaiser who mentioned that Mcafee ScriptScan alone was responsible for more than 15,000 crashes on September 28.

We had 1555 processed crashes on 6.* yesterday, with the 10% throttling rate, this means that roughly 15,000 crashes happened during a single day with this signature!

Something really needs to happen here, do we have any contact with them to get on this fast?

The Blocklist page only lists the block of McAfee ScriptScan on October 3. If you go through the list you find a McAfee SiteAdvisor from March 14.

Users who try to open the McAfee SiteAdvisor add-on page get the same blocked information page though, which means that both add-ons have been blocked by Mozilla.

mcafee scriptscan

mcafee siteadvisor

It is good to see that Mozilla is taking a stand, even if it means to pull add-ons from a big company from the site. It is not the first time that big companies got hit with a block. If you look at the list you will see applications by Microsoft, Yahoo, AVG or Skype on there as well.

McAfee reportedly is working on a fix, according to a moderator response:

1) It’s NOT a security issue

2) It’s a decision made by Mozilla based on crashes that have been reported to Mozilla

3) McAfee is aware of it, has a bug filed and is working with Mozilla to address the problem

4) Until it is fixed, the primary workaround is to re-enable the ScriptScanner. Alternatives include use another browser for now (with most browsers you can import bookmarks and homepages). Also, SiteAdvisor 3.4 will provide *some* overlapping protection, specifically for scripts run in iFrames on webpages

Ed Bott now suspects that McAfee is not solely to blame for the crashes. In his opinion, it is the rapid release process that "plays havoc with the makers of browser add-ons". Bott supports the claim by mentioning that Symantec also experienced compatibility issues in some of their products.

What's your take on the issue?


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  1. EuroScept1C said on October 6, 2011 at 8:13 pm

    There are some guys who want their programs to have a plugin for Firefox. So, they create a Firefox Add-on once and that’s it. They never have intentions to update it anyway.

    McAfee is one of them.

    If you blame Mozilla for trying to improve fast the browser, I blame the other people who aren’t trying at all. I’m glad Mozilla is with me and not on your side.

  2. GiddyUpGo said on October 5, 2011 at 9:35 pm

    Why should McAfee, Norton and others have to modify their programs because Firefox is the only browser that is having trouble?
    Firefox no longer is in the running for the number one browser!
    As a tech, I keep getting requests to remove Firefox from computers. My computer very well could be next. If it were not for the good extensions, that they seem to keep blocking, I would have already been gone.
    Firefox needs to re-start listing to its users!

    1. Martin Brinkmann said on October 5, 2011 at 11:10 pm

      Because it is not really about the browser, but about their users / customers.

  3. Ravi J said on October 5, 2011 at 9:07 pm

    Rapid Release is a really terrible idea. My suspicion (and hope) is that Mozilla will back off of it.

    1. ilev said on October 5, 2011 at 9:56 pm

      Rapid release for fixing bugs and adding features is a great idea, just look at Chrome with its weekly updates. The problem is Firefox’s add-on system which sucks, as there are no such add-on problems with Chrome.

      1. Sandy said on October 12, 2011 at 6:18 am

        Chrome updates every 6 weeks just like Firefox. In fact it’s Google who sold Mozilla on the idea! If Chrome has no problems with updating extensions it’s because their nothing more than glorified userscripts. The potential power of Chrome extensions pales in comparison to Firefox add-ons. If their any problems with Firefox’s add-on system as you say I haven’t seen them. Since Firefox 4 updates have been automatic and flawless. Most add-on developers haven’t had to make any changes and those who did only had minor ones.

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