Mozilla is being accused of creating undue fear and confusion for everyday web surfers, due to the new security feature in Firefox 3.0 that throws out a warning page when a website's SSL certificate is expired or has not been issued by a trusted third party.

Critics say that Firefox 3.0 makes it difficult to set exceptions for certain websites, and is forcing website operators to do business with specific vendors of SSL certificates or risk the appearance that their websites are broken.

Browsers require SSL certificates to initiate encrypted communications and to validate the authenticity of a site. The website, where Firefox 3.0 can be freely downloaded, defends the new feature, saying SSL certificates not issued by a validated certificate authority - so-called self-signed certificates (SSC) - don't provide even basic validation; and expired certificates should not be viewed as "harmless" because they open avenues for hackers.

Mozilla officials say the new feature helps curb electronic eavesdropping or so-called "man in the middle" attacks.

The certificate issue is cropping up on such major sites as the US Army's, which uses certificates issued by the Department of Defense. In the Army's case, Firefox does not recognize the DOD as an authorised certificate provider. Firefox, therefore, rejects the Army site's certificate and defaults to a web page showing a traffic-cop icon and proclaiming "secure connection failed" and that the site's certificate cannot be trusted.

The problem also has surfaced with expired SSL certificates on such sites as Google Checkout and LinkedIn. The issue also could crop up on intranet sites that use SSCs and force IT administrators to configure exceptions within the browser or other workarounds.

Some are saying that Firefox 3.0 is out of line.

The blog this week took Mozilla to task, saying the issue could affect tens of thousands of sites. "People most in need of a clear and explicit warning regarding SSL certificates are inexperienced users, and those are not very likely to understand the error message that Firefox 3 is displaying. A large portion will simply be scared away, thinking that the website is broken," according to the blog.

Developer Nat Tuck called the Firefox feature bad for the web in a blog post he wrote on 31 July. "Mozilla Firefox 3 limits usable encrypted (SSL) websites to those who are willing to pay money to one of their approved digital-certificate vendors. This policy is bad for the web."

Tuck concedes that the SSCs provide no value for authenticating a website, but he says Firefox is ignoring the encryption capabilities of SSL certificates, which thwart snooping on web traffic. He even goes so far as to suggest perhaps open source advocates should create a derivative of the open source Firefox code that includes full SSL functions. officials says SSCs have been treated as "disconcerting" for some time by the open source browser and what changed in Firefox 3.0 is an attempt to make users understand the potential consequences of accepting such certificates.