it may be more to do with your security related software. please list the security software in use with full names and versions, and say what the exact messages are.

Is this only on the outlook site ? or is it on most sites that use secure connections and have https in the link ?

Also see

• How to troubleshoot security error codes on secure websites
• Secure connection failed and Firefox did not connect
• How do I tell if my connection to a website is secure?

The gray lock with yellow/orange triangle is a "mixed content warning." Firefox loaded the page itself securely, and all the most critical assets in the page, but one or more images were loaded over an HTTP connection instead of HTTPS.

This problem can be caused by ads or by media in messages. None of the ways of dealing with this issue is perfect:

• Block insecure content: you may miss things you want to see
• Allow the content and live with the warning icon: you have stress
• Allow the content and turn off the warning: you may forget about mixed content (also, Firefox might not have this option)

More information on mixed content blocking and warning: Mixed content blocking in Firefox.

Now, I should mention that some junk add-ons that insert extra ads into a page may trigger a mixed content warning. Every so often I suggest checking your add-ons for anything you don't recognize.

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then cast a critical eye over the list on the right side. All extensions are optional. If in doubt, disable. If you have questions about any of them, feel free to ask.

Thanks very much for your prompt responses! I haven't got rid of the problem (i.e. I still see the 'mixed content warning') but you got me looking more carefully at exactly when the grey padlock warning appears. It only shows when I select certain emails in my inbox list. Other emails, including ones from this forum, do not switch on the warning, but quite a lot of my other emails do! (Once the warning has been triggered it stays on for all emails, until you clear it by reloading the page.)

At least this shows that in my case it's not the adverts doing it (because all my emails have similar ads in the side panel) but particular content in some of the emails themselves. I'll keep on investigating!