Technology Support Center
Firefox gives security errors when trying to opt-in Windows Live.
To fix this add a security exception to Firefox.
Windows Live works best with Microsoft Internet Explorer. If you wish to use the Mozilla Firefox browser, you will need to add a security exception to your browser settings. The following instructions indicate the procedure. (Note the images may look a little different depending upon what version of Firefox is being used.)
1. Upon clicking the Opt In link, Firefox users will see this screen: 
2. Click the Or you can add an exception? link to expand to reveal more options:
3. Click the Add Exception? button near the bottom of the page:
4. In the dialog box above you see the website for which the exception is to be made. Click Get Certificate button for more options:
5. In this dialog box, click on the Confirm Security Exception button to add the exception to Firefox and proceed to the opt-in website.
6. At this dialog box, click on the Confirm Security Exception button to add the exception to Firefox and proceed to the opt-in website.