Firefoxsometimes takes awhile to close. Periodically have to end process via task manager. 'Any ideas?

Question

I close Firefox. It immediately closes and disappears from the task bar. At times, if I try to open it within 5 or 10 seconds after, it will display a message that '....Firefox is already running......' and will not launch Firefox until waiting for a few more seconds. In the last couple days, it has appeared to be closed when I close it (same scenario as above). But it is saying it is still open for an extended period of time - 30+ seconds. So I go into task manager and end the process. Then it will launch.

Answer 1

-> Tap '''ALT''' key or press '''F10''' to show the Menu Bar
-> go to Help Menu -> select '''Restart with Add-ons Disabled'''
Firefox will close then it will open up with just basic Firefox. Now do this:
-> Update ALL your Firefox Plug-ins https://www.mozilla.com/en-US/plugincheck/
-> go to View Menu -> Toolbars -> '''Menu Bar''' and '''Navigation ToolBar''' -> unselect All Unwanted/Incompatible Toolbars
-> go to Tools Menu -> Clear Recent History -> '''Time range to clear: select "EVERYTHING"''' -> click Details (small arrow) button -> place Checkmarks on '''Cookies, Cache''' -> click '''Clear Now'''
-> go to Tools Menu -> Options -> Content -> place Checkmarks on:
1) Block Pop-up windows 2) Load images automatically 3) Enable JavaScript
-> go to Tools Menu -> Options -> Security -> place Checkmarks on:
1) Warn me when sites try to install add-ons 2) Block reported attack sites 3) Block reported web forgeries 4) Remember Passwords for sites
-> go to Tools Menu -> Options -> Advanced -> Network -> Offline Storage (Cache): click '''Clear Now''' button
-> Click OK on Options window
-> click the Favicon on SearchBar -> click '''Manage Search Engines''' -> select all Unwanted Search Engines and click '''Remove''' -> click OK
-> go to Tools Menu -> Add-ons -> Extensions section -> REMOVE All Unwanted/Suspicious/Incompatible Extensions (Add-ons) -> Restart Firefox
-> go to Tools Menu -> Add-ons -> Appearance section -> REMOVE All Unwanted/Suspicious/Incompatible Themes (Persona) -> Restart Firefox
You can enable your Known & Trustworthy Add-ons and Themes later. Check and tell if its working.