When I open any link in Mozilla browser. It shows a dialogue box  saying that my security certificate is expired. It proceeds when clicked on "Ignore and proceed" and when clicked on "get certificate" it gets certificate and then proceeds. I want to know what is the problem behind this? Why this error is showing to me ?
My Mozilla shows certificate expired warning
Dear Aditya,
Usually "Security certificate has expired" error occurs due to incorrect date/time settings in your windows.
Just check the date and time in lower right corner of your computer and if they are altered, correct them.
Sometimes it happens that when you restart the computer or turn on the computer after some time, Time/Date changes to a previous date. This happens because "cell" inside the "CPU" or laptop (which cares and keep time and date updated even when we turn off the computer) has drained fully and is not chargeable. Its solution is to change the cell by yourself or any computer technician.
If this is not the case with you then please contact here again with snapshot / picture of error message so that a more detailed answer could be provided.