i have installed Web developer toolbar and it was working fine..Now it's not visible and couldn't access developer menu. And i reinstalled the plug-in still the same problem..
I had that problem, too, and none of the solutions I found worked. So, I uninstalled all my add-ons and disabled all plugins. Then, I reinstalled Web Developer and it worked perfectly. I do not know which it was, but one of the other add-ons or plugins was causing the conflict. Just upgraded to 3.6.15 and everything still works.