Steve85b

Try it out on your free dummy site: Click here => <a href="https://tastewp.com/plugins/http-https-remover" rel="nofollow ugc">https://tastewp.com/plugins/http-https-remover</a>. 
(this trick works for all plugins in the WP repo – just replace “wordpress” with “tastewp” in the URL)
UPDATE: This plugin will be maintained again! It changed ownership and we’re currently collecting ideas how to further improve it. If you have any cool ideas, please let us know in Support Forum. Thank you!
Major updated in the latest release (3.0): 
– Plugin has a proper settings page now 
– Many bugs fixed 
– Code optimized, causing performance to increase a lot
Main features:
<ul>
<li>Works in Front- and Backend</li>
<li>Makes every Plugin compatible with https</li>
<li>Compatible with WPBakery & Disqus</li>
<li>Fixes Google Fonts issues</li>
<li>Makes your website faster</li>
</ul>
<h4>What does this Plugin do?</h4>
With protocol relative url’s you simply leave off the http: or https: part of the resource path. The browser will automatically load the resource using the same protocol that the page was loaded with.
For example, an absolute url may look like
<pre><code>src="http://domain.com/script.js"
</code></pre>
If you were to load this from a https page the script will not be loaded – as non-https resources are not loaded from https pages (for security reasons).
The protocol relative url would look like
<pre><code>src="//domain.com/script.js"
</code></pre>
and would load if the web page was http or https.
Tipp: Check your Settings -> General page and make sure your WordPress Address and Site Address are starting with “https”. 
Add the following two lines in your wp-config.php above the line that​ says “Stop Editing Here”:
<pre><code>define('FORCE_SSL', true);
define('FORCE_SSL_ADMIN',true);
</code></pre>
<h4>What is Mixed Content?</h4>
Mixed content occurs when initial HTML is loaded over a secure HTTPS connection, but other resources (such as images, videos, stylesheets, scripts) are loaded over an insecure HTTP connection. This is called mixed content because both HTTP and HTTPS content are being loaded to display the same page, and the initial request was secure over HTTPS. Modern browsers display warnings about this type of content to indicate to the user that this page contains insecure resources.
Note: You should always protect all of your websites with HTTPS, even if they don’t handle sensitive communications.
<h4>Example</h4>
Without Plugin: 
 src=”http://domain.com/script01.js” 
 src=”https://domain.com/script02.js” 
 src=”//domain.com/script03.js”
With Plugin: 
 src=”//domain.com/script01.js” 
 src=”//domain.com/script02.js” 
 src=”//domain.com/script03.js”
<h4>If using Cache Plugins</h4>
If the plugin isn’t working like expected please purge/clear cache for the changes to take effect!

SSL Mixed Content Fix

This is really simple plugin and easy to configure. It works fine and really useful.

Awesome Plugin

A fix for mixed content! This Plugin creates protocol relative urls by removing http + https from links. Works in Front- and Backend!

JS Morisset

A simple, safe, and reliable way to force HTTP URLs to HTTPS dynamically:
No setup required – simply activate the plugin to force HTTP URLs to HTTPS.
There are no plugin settings to adjust, and no changes are made to your WordPress configuration.
SIGNIFICANTLY FASTER than other popular plugins of this type:
Other well known plugins use <a href="https://secure.php.net/manual/en/function.ob-start.php" rel="nofollow ugc">PHP’s output buffer</a> to search & replace URLs in the rendered HTML, which is a technique that is error prone and negatively affects caching performance (as changes are not cached).
This plugin uses standard WordPress filters instead of PHP’s output buffer for maximum reliability, performance, caching compatibility, and uses 301 permanent redirects for best SEO results (<a href="https://en.wikipedia.org/wiki/HTTP_301" rel="nofollow ugc">301 redirects are considered best for SEO when moving from HTTP to HTTPS</a>).
Supports advanced proxy / load-balancing HTTP headers:
<ul>
<li><code>X-Forwarded-Proto</code> (aka <code>HTTP_X_FORWARDED_PROTO</code> server value)</li>
<li><code>X-Forwarded-Ssl</code> (aka <code>HTTP_X_FORWARDED_SSL</code> server value)</li>
</ul>
See <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-Proto" rel="nofollow ugc">Web technology for developers > HTTP > HTTP headers > X-Forwarded-Proto</a> for more details.
<h4>Plugin Requirements</h4>
Your web server must already be configured with an SSL certificate and able to handle HTTPS connections. 😉

JSM Force HTTP to HTTPS / SSL – No Setup, Fast and Reliable

No setup required - simply activate to force HTTP URLs to HTTPS using native WordPress filters and permanent redirects for best SEO.

SSL Mixed Content Fix vs JSM Force HTTP to HTTPS / SSL – No Setup, Fast and Reliable