Mozilla has moved to block the McAfee Firefox extension ScriptScan and has added it to its blocklist. This means that users are prevented from installing it from the Add-ons Mozilla site and that it will be disabled for Firefox and SeaMonkey users that already have it installed.
It's a softblock, meaning that users will be allowed to re-enable the add-on, at their own risk, if it hasn't been causing any problems for them.
Mozilla has explained that the add-on has been the source of a very large number of crashes in the last week and that the issue is affecting both Firefox 6.0.2 and Firefox 7 users.
"McAfee ScriptScan has been blocked for your protection," the Add-ons Mozilla page that housed the extension now reads. "This add-on causes a high volume of crashes." The block is for all ScriptScan versions equal or below 14.4.0.
"We had 1555 processed crashes on 6.* [Firefox 6] yesterday, with the 10% throttling rate, this means that roughly 15,000 crashes happened during a single day with this signature!," Mozilla's Robert Kaiser wrote in one of the bug fillings related to the issue.
Blocking an add-on, even a softblock, is a rather extreme step that Mozilla only takes when the circumstances call for it. With this bug affecting tens of thousands of users, perhaps more, the damage was too great to let it slide.
McAfee has acknowledged the issue and is working internally and with Mozilla to fix the problem. Once an updated version arrives, users will once again be able to install and run the add-on, Mozilla has only blocked it up to version 14.4.0, the one causing the issues.
While some are quick to blame Mozilla's rapid release cycle for the problems, it doesn't seem to have played a role as it affects both the older Firefox 6.0.2 as well as the latest Firefox 7. What's more, the issue showed up after Firefox 6 was launched, indicating that it is linked to an update of the add-on rather than the browser.