1. No it should not be as you did the right thing by using the task menu to shut down Firefox.
2.As Far As I know there is no way to disable auto recovery without Firefox running. How ever this is the link to explain on how to disable it:
The best thing for you to do is to clear out all of Fire fox private data cache. The easiest way (without starting Fire Fox) is to use a program called CCleaner. If you go this route please do the fallowing: GO to Options > settings > Secure Deletion. Set it for NSA or Gutmann. Next go Advanced, Unmarked the box that says "Only delete files in Windows Temp folder older than 24 hours." After that is done go to Cleaner have it Analyze everything but 'wipe free space' or have it scan only for the Firefox files. after that click on run cleaner.
hope this helps you.
While I was browsing the web, a pop up called Security threat analysis showed up. I opened up task manager and closed firefox from there. But, whenever i reopen firefox, it recovers back to the pop up. I scanned my computer with Malwarebytes and Microsoft security essentials both coming up with nothing. My question is
1. Is my computer infected?
2. Can I disable firefox's auto recovery feature without opening firefox?