After some days of my PC running, Firefox starts to show the Secure connection error message with a code: SEC_ERROR_BAD_SIGNATURE, instead of up to that moment frequently and correctly opened (secure) web pages. The only action that helped was to delete the file cert8.db (see Firefox Menu/?/Technical information/Profile folder), but after some time (usually days, a week or two) the error behaviour of Firefox repeats again. Is there any system solution? I am sure deleting the file cert8.db is neither stable nor safe way how to do it - one can delete something else by mistake... Thanks.