much like airport security, it is difficult to achieve both at the same time. :-)
there may be addons that will help you surf more efficiently and effectively. but you'll have to know more about your own surfing habits to choose wisely.
security starts with noscript at the top of the list. with adblock plus, you have to notice the offending ad and block it to be effective. some offending ads aren't blockable. therfore, while it works, it "slows" down the surfing experience.
i also use flashblock, betterprivacy and ghostery. with flashblock, flash objects aren't automatically played, using up resources. they stay dormant until or unless you activate them. i'll let you investigate ghostery and betterprivacy on your own.
arguably for the paranoid, or those that really just hate java based advertising popping up or appearing on your favourite websites, but for security, you really cant beat the 'No-Script' plugin for Firefox for high level security, which you can get here click here
As Bill10 has mentioned, to stop unwanted adverts and pop ups from appearing, you may want to also use Ad-Block Plus, another plugin for Firefox, click here