Having an browser installed does not make a PC any less or more secure, it has been proven recently that most versions of IE have major vulnerabilities (just ask Google).
Really? Having any random browser installed does not make a PC any less or more secure? Please, please tell me you are not in any way affiliated with any environment subject to federal regulations.
Prime example:
Let us say your environment is exclusively a MS shop. You have all the development resources, security resources, and vendor support to ensure that environment is safe, secure, and compatible with your applications. Then, bam, a problem shows up. Joe User cannot use X web application. Security starts seeing strange traffic coming across the network, traffic that is malicious in nature. Lo and behold, that is because Joe User installed a browser not supported within the organization, which, in this case, happens to be copy of Firefox 3.5 (http://www.mozilla.org/security/known-vulnerabilities/firefox36.html). Suddenly, your organization has just been hacked, corporate data is being siphoned off the network, federal regulators are crawling down your boss's throat, the organization gets hit with a huge fine and other costs related to the data breach, and why?
Because you believed that installing any old browser on any system in any environment doesn't make the PC any more or less secure.
Moral of the story? Don't be a fucking idiot, and understand the need for prioritization and standardization within a corporate network, especially one of those corporate networks that is subject to regulatory oversight regarding information technology.
We are each entitled to our own opinion, but no one is entitled to his own facts. -- Patrick Moynihan