The SSL Insecure Content Fixer plugin does not make any changes to your website. It cleans things up on-the-fly. It’s an easy way to get a site working on HTTPS quickly, or to fix up some plugins / themes that misbehave. If you deactivate the plugin, it stops working.
If you have content that needs fixing, my plugin will cover you while you get ready to clean up the content. Once you’re ready to fix the content on your website permanently, read about cleaning up your HTTP content for HTTPS.
If you needed to change the HTTPS detection method so that your website could detect when it was loaded over HTTPS, then you might be able to make that permanent too by editing your
wp-config.php file. Developers only!