What secure site? You don't mean support.mozilla.org, do you? There shouldn't be any insecure content here.

1. Press Ctrl+Shift+K to open the Web Console. See the following article for usage details.
   • https://developer.mozilla.org/en-US/docs/Tools/Web_Console
2. Press the Clear button.
3. Load the problematic page. For things like images, you'll see entries that say "Loading mixed (insecure) display content on a secure page" followed by the URL of the resource in question. I'm not sure what the verbiage is for blocked scripts. I'd guess if there's too much in the console to sort through, you can probably find what you're looking for by typing mixed into the search box in the top right.

If you get the "shield" icon to the left of the padlock in the address bar, it's considered active content with more potential to cause leakage of private data or other mischief. This article discusses: Mixed content blocking in Firefox

If you get the "gray exclamation triangle" icon in place of the padlock, the blocked content most likely is an image, although it could be some other kind of display content. Another console you can use to check for mixed content is the browser console (Ctrl+Shift+j). You can leave that open as a separate window (minimized or otherwise out of sight) with "mixed" in the search box and switch over to it when you get curious.

@Gingerbread Man Thanks. I'm kinda new in developing SSL-secured websites. The blocked content were some images and a Google Font.