µBlock is a popular ad-blocker for Chrome and now available on Firefox (well its initial versions for now). This ad-blocker has smaller memory overhead compared to Ad Blocker Plus. ABP consumes much memory as it injects a huge style sheet into every page you visit, in order to implement element hiding. That style sheet contains thousands of CSS rules that are pretty much always the same for every page, whether or not that page actually needs any of those hiding rules. µBlock, on the other hand, will identify (by surveying) which element hiding rules are needed by the website you are visiting and will only inject the required element hiding rules. So instead of having thousands of additional CSS rules that the browser needs to parse for every page you visit, you end up with only a handful of rules that the page actually ends up using, keeping memory usage extremely low. Moreover surveying and injecting smaller CSS is less CPU intensive compared to injecting heavy CSS...