Noscript and Noflash for example let you control whether things like javascript or flash videos run on a case by case basis.
This is already built into IE 5 and newer.. it is the security settings.
Have you used Firefox with Noscript? There is no comparison in this functionality. Firefox can do the same without Noscript as well, but also in the settings dialogs, and not nearly as flexible.
I think what the original article was trying to say in over-simplified terms, is that Firefox has a lower barrier to add-ons (which include extensions and plugins), because many
extensions can be written entirely in javascript or XUL. This is both its strength and its weakness. (I despise javascript) This approach may very well eventually be the downfall of Firefox, as much of the application itself is written in javascript.
Anyway, if you want to create a
plugin to Internet Explorer (or Firefox), you're writing a dll in C, C++, C# or VB, and you'll actually have to compile it! The Horror!
Overall you will find better quality plugins for IE because of this, where you will find a lot more firefox extensions of lower quality. Though sometimes a quickie firefox javascript extension is all that is neeeded to do the job where a dll plugin would be overkill.
Definintions:
Addon = A plugin or an extension.
Extension = a firefox javascript/xul addon (which can call a dll if needed)
Plugin = an actual dll with platform native executable code addon.
The difference is not that obvious, and often confused.