This is an option in Outlook 2013. Quick way to check if email is spam or worse.
Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.
The link target is already shown in the status line, when you hover with the mouse over the link - is that not enough?
Are you referring to Tooltip?
In case you're wondering, Thunderbird displays the link information in the "Status Bar".