Mozilla today upgraded Firefox to version 49, and said it is expanding the pool of users who receive the multiple process browser that started reaching a few customers weeks ago.

"In this release, we're expanding support for a small initial set of compatible add-ons as we move toward a multi-process experience for all Firefox users in 2017," Nick Nguyen, who leads the Firefox team, wrote on a company blog.

On Aug. 3, Mozilla began pushing a multi-process Firefox to some users.

The effort, code-named "Electrolysis" (shortened to "e10s"), separated Firefox's operation into more than one CPU process. The practice lets the browser take advantage of multi-processor systems for better performance, and segregates the browser's user interface (UI) and content to keep Firefox from fully crashing when a website or web app fails.

Other browsers, including Apple's Safari and Google's Chrome, already support multiple processes, albeit differently. Safari relies on a single process for the rendering engine, then spawns a new process for each tab's content. Meanwhile, Chrome assigns a new rendering process to each new tab.

Mozilla will eventually get to a Safari-style model, but the open-source developer is moving there in measured steps. Today's Firefox 49 was the second, and is to be followed by November's Firefox 50, which will further expand the multi-process audience.

The e10s edition of Firefox 49 will be offered to those users who only run one or more of a small number of third-party browser add-ons that Mozilla has identified as compatible with the process separation. Firefox 50 e10s will reach even more users as Mozilla gives the green light to a larger group of add-ons.

Mozilla's goal is to turn on e10s for all Firefox users with version 51, now slated to launch Jan. 24, 2017.

According to Mozilla's latest published status report, the e10s version of Firefox was being used by approximately 20 million users daily as of Sept. 6.

Also on Tuesday and as of Firefox 49, Mozilla dropped support for OS X 10.6, 10.7 and 10.8, the very-over-the-hill editions better known as Snow Leopard, Lion and Mountain Lion, respectively. Apple no longer supports those operating systems -- which debuted between 2009 and 2012 -- with security updates.

Firefox 49 can be downloaded for Windows, OS X and Linux from Mozilla's website.