Mozilla is making the death of Firefox 3.5 a priority, and this should not be a real surprise, considering the last update to the open source browser released at the end of April 2011. Version 3.5.19 released last month is the last update that will be delivered to Firefox 3.5. Customers have two new versions of Firefox that they can upgrade to, and in fact, Mozilla is encouraging this. The open source browser vendor advises customers to make the jump to either Firefox 4.0 or Firefox 3.6, but to definitely hurry up and move off of Firefox 3.5. “We need a plan to obsolete Firefox 3.5 as we can't support it into perpetuity. We have been frustrated with our efforts to move users off of old releases and are worried too many people do not upgrade and are on vulnerable and unsupported versions of Firefox,” Mozilla said. The company estimates that the number of Firefox 3.5 users has dropped dramatically, although apparently there are quite a few still running it, approximately 12 million. Mozilla wants to kill Firefox 3.5 as fast as possible, and although it would prefer that customers upgrade to Firefox 4.0, it’s willing to settle for Firefox 3.6 upgrades as well. In this regard, Firefox 3.6 could be served as an automatic upgrade to all Firefox 3.5 users that have automatic updates enabled but did not make the jump themselves until now. “We have no intention to release another 3.5 update (but if we need a chemspill before the plan is implemented we will discuss it),” noted Christian Legnitto, Firefox release manager. “The end result is sending 3.6 as a minor update for 3.5 users (…).No real actions need to take place until June, so there aren't pressing requirements that could impact the new release process.” Mozilla will release Firefox 5 in June 2011, after which it will provide new major versions of the open source browser approximately once every six week. With the company giving green light to automatic upgrades, every new major Firefox release will only be supported until its successor is made available, with the exception of Firefox 4.0 and Firefox 3.6 which will continue to enjoy support per the old release model.