Developer Adblock Plus: high memory usage is partly due to bug in Firefox

The maker of Adblock Plus, a popular ad-blocking add-on, has responded to a study that found the extension can cause very high memory usage in Firefox. The problem is acknowledged, but a bug in Firefox in particular is said to play an important role.

Australian programmer Nicholas Nethercote published a blog post this week exposing the memory hunger of the Adblock Plus add-on. By default, the extension already claims 60 to 70MB when just enabling Adblock Plus. In addition, each iframe, a container in which advertisements are often placed, costs approximately 4MB. Because web pages can host large numbers of iframes, Firefox’s memory usage can quickly add up with Adblock Plus activated.

When loading a test page with more than four hundred iframes, Firefox’s memory hunger rises to more than 2GB. The page also loads slowly. Without an adblocker, Firefox would ‘only’ claim 370MB and the processing will be faster. The programmer therefore wonders whether the builders of Adblock Plus can implement optimizations in their add-on.

The developers behind Adblock Plus have now formulated an answer to this question. For example, part of the considerable memory consumption could be explained by the way Firefox works, which they see as a bug. When Adblock applies a stylesheet to an element to hide it, Firefox always makes a copy of the stylesheet behind the scenes. The developers hope that Mozilla can squash this bug in future Firefox versions.

Adblock Plus itself could also be improved. For example, the makers want to build in an evaluation option that can be used to determine which filters are effective and which are not. Infrequently used filters can then be removed, increasing speed and potentially reducing memory consumption. Currently, the add-on contains about fifty thousand filter rules.