or if you want overall security, no scripting by default, but the ability to on a case by case allow it for safe know sites (create your own white list for example), install a plugin call 'noscript'. By far better than all the suggestion above.
http://noscript.net/
Also, if you don't want certain banners/pictures being displayed on certain sites in firefox, just right click on the banner/pic and from the context menu select 'block images from xxxxxxxxx.xxx'
