Browsers are among the most memory-consuming programs the average user can run on their computer and while the likes of Google and Mozilla can optimise the heck out of Chrome and Firefox, the multimedia-heavy web of today is always going to demand a lot of storage, be it in the form of RAM or disk space. Of course, whacking a bunch of extensions and add-ons isn't going to help things, but could a single, extremely popular one designed to block ads be responsible for hogging gigabytes of memory?
Almost from its inception, Mozilla's Firefox has been a target for criticism over its memory usage, though it's certainly not alone. The multi-process design of current browsers requires more overhead than a single-process approach, but the benefits of the former -- increased security, isolation from page crashes and better memory reclamation -- usually outweigh the cons.
These days, as long as you keep your tabs under control, browsers won't gobble up all your available memory. However, introduce a few misbehaving add-ons and things can get out of control.
Mozilla decided to put a popular one to the test -- Adblock Plus. ABP is designed to not only prevent advertising from showing on web pages, but formatting those pages so the lack of ads doesn't significantly disturb the layout. Unfortunately, this behaviour comes at a cost.
As Mozilla's Nicholas Nethercote discovered, ABP can add gigabytes to Firefox's memory usage, under a worst-case scenario where a page heavily features iframes. More typically, it can add hundreds of megabytes, which is still pretty bad.
Adblock Plus developer Wladimir Palant responded to Mozilla's findings by admitting that the add-on can consume more memory than it should, because it creates a stylesheet each time a new page is loaded. When there's an abundance of iframes (which are essentially a page within a page), this can get out of control. Palant states this is a bug with Firefox, rather than Adblock Plus.
That said, Palant says that ABP could stores it filters more efficiently, and work to remove ""unnecessary memory consumption" is ongoing.
So ultimately, who's at fault? Both parties it seems. Even optimised, Adblock Plus' functionality will always come at the price of speed and memory, despite the fact it's removing content from web pages. It's up to you whether the hit is worth it.