This is a bug in Firefox and developers believe that this issue has been fixed in Firefox 30 beta 8. You can either wait for the fix to hit the Release channel or you can download Firefox Beta and test it out yourself. (https://mozilla.org/firefox/beta) Alternatively, this issue is caused by Firefox being set to automatically clear History on exit. Change this setting to the default (Remember history) to see if it still hangs in the Task Manager.

• The image "new fx menu" does not exist. -> Options -> Privacy -> Firefox will [Remember History]

You can also check that you do not run Firefox in permanent Private Browsing mode (Never remember history).

• https://support.mozilla.org/kb/Private+Browsing

• Tools > Options > Privacy > Firefox will: "Use custom settings for history"
• Deselect: [ ] "Always use private browsing mode"

Note that in case automatic updating fails, you can download the newest Firefox version by going to https://mozilla.org/firefox to upgrade Firefox manually

As for your hang with Flash, I'm pretty sure everyone is fed up with Flash but Mozilla is working on an alternative called Shumway. It's currently in the Nightly build of Firefox although it doesn't work as of yet and the pref to enable it (shumway.disabled) is set to true meaning Shumway doesn't come enabled automatically. You can check out Shumway below. Note: Shumway is not meant to be used as a replacement to Flash. It's very unstable and videos do not even play.

• http://mozilla.github.io/shumway/

You can try to disable protected mode in Flash. Try to disable Protected Mode in Flash 11.3 and above by adding the line ProtectedMode=0 to the Flash "mms.cfg" file located in one of these locations: [46]

   (Windows 32bit) C:\Windows\System32\Macromed\Flash 
   (Windows 64bit) C:\Windows\SysWOW64\Macromed\Flash 

For example, on a Windows 7 64-bit system, open the C:\Windows\SysWOW64\Macromed\Flash folder, copy the file "mms.cfg" to the desktop, open it in Notepad, add a new line ProtectedMode=0 and then close Notepad, saving your changes. Next, go back to the C:\Windows\SysWOW64\Macromed\Flash folder, rename the original file to "mms.cfgBAK" (to save it as a backup) and then drag and drop in the modified "mms.cfg" file from the desktop.

Note: To re-enable Flash Protected Mode, either restore a backup of the original mms.cfg file, if you saved one, or else re-edit the mms.cfg file to remove the ProtectedMode=0 l line you added. Updating Flash Player or installing a newer version does not automatically re-enable Protected Mode

So, to fix the current issue, I have to turn off 'features' of FF that protect my privacy. I quite literally laughed out loud at that one xD

Thank you for your quick response.

Like I said, this is a BUG. You're welcome to try out Firefox Beta and see if the issues persist. Others have reported success with Firefox Beta and are unable to replicate the issue. If you decide to try this out, please let me know if it works so if it doesn't, developers can gather feedback

A developer who worked on the bug had this to say

Note I'm one of the devs who fixed the issue. We believe that the issue has been fixed in Firefox 30 beta 8. If you are affected by the issue, you may download this version here: https://www.mozilla.org/en-US/firefox/channel/ or wait a few weeks until it comes out of beta. This bug was triggered by cleanup of thumbnails during shutdown. In most runs of Firefox, this cleanup worked nicely. However, a combination of circumstances could cause the cleanup mechanism to start loading its resources during shutdown, after the loading mechanism had already shutdown itself. Firefox waited until that load was complete to proceed with shutdown, but the load could not complete. Two fixes have been landed. A fix specific to thumbnails landed in time for Firefox Beta 8 and ensures that we never shutdown the loading mechanism before the cleanup has had a chance to complete. A more general fix will has landed shortly after to ensure that the bug does not reappear with other subsystems. You may find all the technical data on the bug and how it was resolved here. As a side-note, this issue is not considered a security bug, as it may only be triggered by sitting in front of the computer and changing the settings. We reserve the denomination for security bugs for issues that can be triggered without the consent of the user.

I have installed 30.beta and will let you know if the problem persists.

Thanks again.

Now we just have to wait for the flash video thing to get sorted. Good luck with Shumway Mozilla!