"Remember password for sites" option is each time disabled after I open Firefox

Hi... For some reason in the "Security" icon the "Remember password for sites" option is each time disabled after I open Firefox, even if a have enabled it the last time when it was used. So, if a new site is prompting for Username and Password the browser does never bring the password manager tool bar to pop-up due to this (unless I enable it again i.e. tick on "Remember password for sites"). For already used sites Firefox does not fill in the Password automatically either. In "Exceptions" there is no website listed, in the "Privacy" icon the "Remember history" is enabled, means I am never in the "Private browsing mode". I am using VIPRE Antivirus, CCleaner, but they are not set to clean any history automatically. Have even re-installed Firefox, but no changes. The former used passwords are saved in "Saved passwords". Appreciate an advice.