Application installer add extention to my browser. Is mavericks following the path of Windows? I have use OS X 10.6.8 for years and just recently did a fresh installation of Mavericks. One of the nicest aspects of OS X was the fact that after three years of use and installing tons of application, none of them, ever added any toolbar or extension to my firefox. As appose to windows that after couple of weeks, the browser looks like a circus.

Today during installing uTorrent on Mavericks, I noticed that my firefox was reset and upon opening my home page changed to yahoo as well as my default search engine. Later I noticed that it has also added an extension to my browser.

Is this a flaw in the Apple new OS? Was it always there and I was just lucky in three years of using Snow Leopard? Is there some kind of security mechanism that I have to enable?
During installation many installers, not just uTorrent. (Also Daemon Tools for example on Windows) try to install a lot of stuff on your computer.

If you accept one of the offers (which looks like an agreement), you end up with stupid plugins in your browser and other default search tools - this is exactly what you're facing right now.

I would strongly recommend you to open the installer again and notice the 3rd party installers which are hidden inside the uTorrent installation program so you can spot them in future installations.

For now, to fix this problem: Remove the toolbars / plugins manually and set back Google (or whatever your default search provider was) as default search engine.

To make this answer complete, the same could happen to you on Snow Leopard. This is just the way the installer (ab)uses the way you grant access in installing an application as Administrator.