when email opened browser changes to unsecured site and caution sign appears
only in the mozilla browser does this happen. does not happen in the chrome browser I sign into my yahoo email. the green lock is in the taskbar when I open any email it changes to grey lock and a yellow caution sign appears telling me the site is not secure.
This will be caused by emails which embed content (like an image) that is loaded through a http-connection. The grey lock with the yellow warning still means that the data you view and enter on the site is secure and only transmitted to yahoo.
You can also set up firefox to block the loading of http-elements like images on an otherwise encrypted https-site - then the green lock should always stay in place on your mail: enter about:config into the Firefox address bar (confirm the info message in case it shows up) & search for the preference named security.mixed_content.block_display_content. double-click it and change its value to true.
Hope this helps!