Check this blog may be it is helpful to solve your problem.
What is Mixed Content?
When a user visits a page served over HTTP, their connection is open
for eavesdropping and man-in-the-middle (MITM) attacks. When a user
visits a page served over HTTPS, their connection with the web server
is authenticated and encrypted with SSL and hence safeguarded from
eavesdroppers and MITM attacks.
However, if an HTTPS page includes HTTP content, the HTTP portion can
be read or modified by attackers, even though the main page is served
over HTTPS. When an HTTPS page has HTTP content, we call that content
“mixed”. The webpage that the user is visiting is only partially
encrypted, since some of the content is retrieved unencrypted over
HTTP. The Mixed Content Blocker blocks certain HTTP requests on HTTPS
What do I mean by “certain HTTP requests”? Why wouldn’t the Mixed
Content Blocker just block all HTTP requests? To answer this
question, I will first explain how the browser security community
divides mixed content into two categories; Mixed Active Content and
Mixed Passive Content.