In particularly their is no disable function provided by mozilla. Their might have been ways in previous versions. But now it's Major topic discussed on the internet. Im having the same problem too, im not able to access some websites, and mostly which is dealt with money and trade.

Which security warning are you referring to?
Is that about an untrusted website?

Check the date and time in the clock on your computer: (double) click the clock icon on the Windows Taskbar.

• https://support.mozilla.com/kb/Secure+Connection+Failed