On a vBulletin website Firefox developer tool returned errors:

Blocked loading mixed active content “http://www.facebook.com/widgets/like.php?href=***
Blocked loading mixed active content “http://platform.twitter.com/widgets.js

My site is https:// so it do not like loading http:// only content

i was unable to find above mentioned URLs anywhere inside files, so it was in database and in vBulletin admin area / Settings / plusone

i was able to fix the problem by replacing all src="http: by src="https:

and error is away now