This is a continuation of a thread found here: https://support.mozilla.org/en-US/questions/997448 by Compumind. I reported I was having the same experience, especially when opening links from emails in Thunderbird. I also reported I was forced to revert to FF 28. Moses replied in above thread and suggested: (1) Download a fresh installer from https://www.mozilla.org/firefox/all/ to a convenient location. (Scroll down to your preferred language.) (2) Exit out of Firefox. (3) Rename the folder C:\Program Files (x86)\Mozilla Firefox to C:\Program Files (x86)\OldFirefox (4) Run the installer you downloaded in #1. It should automatically connect to your existing settings. I followed these instruction carefully but no joy. Upon installing FF 29, not only would it refuse to exit (using "exit") and remain running in the Task Manager until I killed it after opening links from Thunderbird, but I found it refused to exit after simple browsing and following links. Moses had asked I not reply in original thread so I am re-posting here. I believe this is a serious bug. With Firefox 28...no problems except a minor one I reported here: https://bugzilla.mozilla.org/show_bug.cgi?id=1002089 Again I am forced back to FF 28, though I miss the beautiful interface and security fixes, I need to have a browser that works properly. My wife has never even seen the Task Manager before so this is problem. Besides the "educated guesses" made with this post, the only other thing outside of usual that I do, is to have a security policy regarding cookies (don't accept by default...I make exceptions for cookies I want to retain and have a several that are only "allow for session.") I also have FF set to delete browsing history on exit, but that takes a split second. I look forward to when this issue can be addressed successfully and I am able to use FF 29 (and have it exit properly...I can't expect my wife to follow all these instructions and close it often manually in the task manager...nor do I want to do this.) Good luck on all the Mozilla projects. Having installed FF 29 twice and then reverted back to 28 twice, I am going to wait and see how this plays out. Please don't send me the standard, "start in safe mode", "restart with add-ons disabled", "reset Firefox" (last time that destroyed my browser completely) stuff. I do not believe this is what's happening. Moses added that there is a problem with email notifications going through, so take your time, friends.