Just follow the about:config option. Also, if you’re not already doing so, you need to run an extension such as NoScript. NS allows you to whitelist/blacklist Java and Java script. It’s also granular. Meaning: Some websites can have javascripts from third parties running (google analytics for example) and NS allows you to pick and choose what scripts are allowed to run for any given site.
already run NS and adblock
love ‘em both.