I seen some unexperienced web developers restricting visitors to view their site in all browsers, let me tell they are making a big mistake.
Here are top two reasons why you should let visits view your site in all browsers.
The First: You are losing visitors, according to w3schools.com 47% are using Firefox and the rest of the 53% using something else. Lets just say you designed your site to look unique in Firefox and in the rest of the browsers your design doesn't look that good, so you decided to block other visitors who are not using Firefox. That would mean that you are losing 53% of the visitors.
An example if you are getting 2000 visitors a day and your site can only be viewed in Firefox that would mean you lose over 2000 other visitors who use different kind of browsers. Just think how many visitors you lost over the years that just simply couldn't access your site that could have liked what you got their and maybe even become your loyal visitor.
The Second: IT IS ANNOYING. Especially if you tell them to download the specific browser to view your site. Just think about it, will you be downloading and installing completely different browser if your have been using IE or Chrome forever just to view one website?! I wouldn't and I don't know who actually would. Waist all that time just to discover that your website sucks...... or not.
Here is some food for you thought.
If you know other good reason why not to restrict visitors to view you site in a specific browser please feel free to mention them below.
Just FYI I use Firefox, IE and Chrome.