Solved this myself - question was erroneous, nothing to do with Firefox, it was websites using persist cookies allowing my access, not the Firefox saved logins. Clarified in my original question.(...comments in brackets!)

Original question - I had lots of passwords and usernames for various sites, which until recently have worked fine.(...on a different machine!) Now when I access websites which I know I have passwords and usernames saved for, the fields do not autofill. On checking preferences privacy & security, in saved logins, there are none. (...because I hadn't imported profiles correctly!) However, I have a couple of sites on my bookmarks toolbar, and these site logins are filled in as expected. Where is Firefox finding these logins when I can see saved logins screen empty?(...Firefox isn't - see 1st line!)