What makes FireFox so popular? I will say is because the plug-ins. An excellent platform is the reason why plug-in become the best part of FireFox.
For example, if one of your plug-in is not compatible with your current version of FireFox, you will not be able to download and install. And if you already installed a faulty plug-in, FireFox will disabled it when they confirm the bug and inform you the reason in plug-in management console like this:
AVG SafeSearch, versions older than 8.0, for Firefox 3.1a1 and newer. Reason: breaks a core navigation method (see bug 479095).