Bug 1395539 - Disable toolkit/mozapps/extensions/test/browser/browser_bug591465.js on linux/opt to get tests running in multi-core. r=gbrown

toolkit/mozapps/extensions/test/browser/browser-common.ini

@@ -20,6 +20,7 @@ skip-if = buildapp == 'mulet'
 [browser_bug586574.js]
 [browser_bug587970.js]
 [browser_bug591465.js]
+skip-if = os == "linux" && !debug # Bug 1395539 - fails on multi-core
 [browser_bug591663.js]
 [browser_bug593535.js]
 skip-if = true # Bug 1093190 - Disabled due to leak