thanks, for providing those details. is this happening in a corporate environment?

Yes and when I changed about:config as below, security enterprise_roots.enabled ... modified ... boolean ... true

It works, Is it a good thing to do ? or shall I revert my change ?

yes, that's probably the right solution in this case - you just need to be aware that your network traffic might be scanned and monitored in this environment by your employer.

Thank you

Hi again, were you able to find which certificate causing the issue. May be I can export it from chrome to firefox. I have some pages loading very slow with the enterprise solution. So may be fixing the certificate issue itself would be better if we can.

the information was embedded in your original question. it was some random sounding cert name probably used by some network appliance but i can't remember the details anymore...

edit: exchanged some information via pm