Some time you install fresh Operating system in your computer and then
you install Browser, Mozilla Firefox. After Install you try to open
Gmail,Yahoo or Facebook in Mozilla Firefox but you do not see your
required page and see a message "Server Security Certificate is not yet
Valid" then you also try to open the page by clicking on "Continue
anyway" bu the result is same
infect this problem occurs due to incorrect date and time of your computer. By synchronizing your system clock you can solve this problem.