Some group is advocating blocking Firefox from accessing some sites, and has set up a site to explain their reasons. Their argument is that Firefox provides an easy way to block ads and - get this - watching a site without ads is theft.
Numerous web sites exist in order to provide quality content in exchange for displaying ads. Accessing the content while blocking the ads, therefore would be no less than stealing. Millions of hard working people are being robbed of their time and effort by this type of software.
If I’m not even willing to look at your ads, that means I’m not your target market. If you don’t want your articles publicly accessible, don’t publish them - otherwise you have to consider the people with ad blockers as the cost of playing the game. Or even better: if your stuff is so great then move to a subscription mechanism, and people will likely be happy to pay.
But even leaving such small things as rational concerns and the structure of the web itself aside, blocking Firefox will do you no good: having Firefox pretend to be some other browser is even easier than blocking ads.