Starting today, we’ll be running a 3-week test in Firefox 36 betas which disables protected mode in the Adobe Flash Player. Because this is a significant change in the way Flash interacts with Firefox, I am asking our Firefox beta users on Windows to pay special attention to any unusual problems related to Flash and file bugs for any problems.
Protected mode is a Flash security option for Firefox on Windows which runs parts of Flash within a security sandbox. Every week, more than 20 million Firefox users on Windows are affected by Flash hangs and crashes, and Firefox telemetry data shows that as many as half of these hangs are related to protected mode.
In order to get extended testing, this change is being made for the beta channel now, but will not be part of the final Firefox 36 release. During the beta period, we will be carefully monitoring Firefox telemetry data to confirm our understanding of Flash stability, and watching for problems caused by this change. Disabling protected mode, as with any security feature, is not an easy decision, because it could make it easier to exploit security bugs in the Flash player. Due to the severity of the performance and stability problems, however, I believe this security feature may be harming the Firefox user experience more than it helps.
As part of this change, Firefox will be enabling an early version of its own security sandbox around Flash on Windows. We will continue to develop, test, and improve this sandbox. We also continue to work closely with Adobe to improve this new sandbox as well as fix performance and stability issues with Flash/Firefox integration.