Ubuntu Security Notice 3991-3 - USN-3991-1 fixed vulnerabilities in Firefox, and USN-3991-2 fixed a subsequent regression. The update caused an additional regression that resulted in Firefox failing to load correctly after executing it in safe mode. This update fixes the problem. Various other issues were also addressed.
5c1699b949d86c39c9f8b65e74e1a7f1f5a61db5769f7396a87fc70f10f4d139