A single Firefox process. (credit: Roger)

After seven years of development, version 48 is at last enabling a multiprocess feature comparable to what Internet Explorer and Google Chrome have offered as stable features since 2009. By running their rendering engines in a separate process from the browser shell, IE and Chrome are more stable (a Web page crash does not take down the entire browser) and more secure (those separate processes can run with limited user privileges). In order to bring the same multiprocess capability to Firefox, Mozilla started the Electrolysis project in 2009. But the organization has taken substantially longer than Microsoft, Google, and Apple to ship this feature.

Mozilla’s delay was partly driven by changing priorities within the organization—Electrolysis development was suspended in 2011 before being resumed in 2013—and partly because Firefox’s historic extension architecture made this kind of separation much harder to achieve. Traditional Firefox extensions can invasively meddle with parts of the browser and assume equal access both to the rendering engine and to the browser’s shell. Firefox’s developers had to both create a new extension system (they’ve ended up using HTML-and-JavaScript based extensions closely related to those pioneered by Chrome and also adopted by Edge) and create shim layers to offer developers a temporary way to continue to support their old extensions.