First, please update to Firefox 35. You are running 31 and it is very old and out of date, with dozens of security vulnerabilities. Update Firefox to the latest release

After that, please give us a screenshot of the shield icon.

See also:

• https://support.mozilla.org/kb/how-does-content-isnt-secure-affect-my-safety
• https://developer.mozilla.org/Security/MixedContent

• https://addons.mozilla.org/firefox/addon/toggle-mixed-active-content/

@Tyler Downer: Here is a screenshot of the icon in question: http://i.imgur.com/eFQTyda.png

@cor-el: I have bookmarked this. However, could you please explain how it works, and what I have to do with it, exactly? (aside from download it, that is)

That is the new mixed content blocker built in Firefox, it's meant to protect you from potentially insecure content. You can adjust the settings using the links above.

@Tyler Downer: Ok, thanks. So in short, I guess there's not much I can do aside from the links, lol.

Is there any way you could explain to me what the last link does? I know it has somewhat of an explanation on the page, but I would just like some clarification on what to do with it...

You get the shield when you are on a secure page that has content coming via an open http connection. You can see what content that is in the Web Console (Firefox/Tools > Web Developer). Mixed content should appear as red text. You can reload web page(s) and bypass the cache to generate the log.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

If there is mixed passive content (e.g. images) coming via an open connection then Firefox shows an exclamation mark instead of "Site Identity Button" (globe/padlock) on the location/address bar.

@cor-el or @Tyler Downer, could you please explain what this link here: https://addons.mozilla.org/en-US/firefox/addon/toggle-mixed-active-content/ (The last link Cor-el posted) does, or what I am supposed to do with it?

That extension is for the case of mixed active content like JavaScript and content in iframes. It allows to temporarily disable the blocking of mixed active content by toggling the security.mixed_content.block_active_content pref. Firefox doesn't block mixed passive content (security.mixed_content.block_display_content is false by default), <strike>so you do not need it for your case and it won't have effect</strike>.

So I probably won't need it for Tumblr-related browsings, then?

Did you check via the Web Console (Firefox/Tools > Web Developer) what content is blocked?

I got confused in my above reply because you see the shield and not the exclamation mark and that means that active content is blocked and the extension would help in that case. But it is always best to check what content is being served via an open connection. There shouldn't be content on a secure https page that comes via an open connection.

Dunno if this is the case on other pages, but here's what I got when I checked the page I am currently on: 1) "Error: Permission denied to access property 'toString'" 2)Blocked loading mixed active content "http://platform.linkedin.com/js/cdoCdxsTest.js?rnd=1-1-13960-0-0-19676-706048186-yySkaMPZea4yaYifcaeqIg0OUUhv0aiW2TAmPGu42TAmPGvaWCdiMa5kfqGben8bgnoeaIcjGidabcIjGicGbfaawGOiabaagaaGacGayafQewLUAxqXlMLHzc5ODI5WCM9Kaaaa"

Here's a screenshot, if it helps you better: http://i.imgur.com/t8oYT1x.png