To give you some perspective on things - a website designer called Danny Carlton started it all to block Firefox on his website in order to boycott the Ad Block Plus extension of the browser. Now it seems that many other website owners have joined forces with him.
Firefox has an extension / add-on called Ad Block Plus which blocks most of the advertisements displayed on the website. This feature of the extension has irritated many website owners because the amount of money they receive was reduced since the users discovered the extension. Incase you didn't know this earlier - many of the website owners are receiving important funds from advertisements and now their business is strongly affected.
So Danny Carlton has created a special website called 'Why Firefox is Blocked'. He and many other Web designers / Website Owners need to just implement a special code in their content in order to restrict the access of the Mozilla browser. They are blocking Firefox as a whole since there's no way to block only the Ad Block Plus extension. Danny Carlton and others now fight against the entire application until the add-on is disabled.
I somehow feel(in my opinion) that Danny Carlton is right because many of the Website Owners are able to run and maintain their websites using the funds received from advertising. A website will need a lot of funds even in terms of hosting on dedicated servers, etc. Lets take AdSense, for example - Millions of registered members publish Google Adsense ads on their websites and, every time a visitor to the website clicks on them, a certain amount of money is automatically transferred into his account(although it is very small at most times). Since the Firefox extension blocks most of the ads, the website owner doesn't receive any money.
So let's watch out how this issue turns out in the end.