Firefox doesn't store your email or contacts, it displays that data from the webmail server that you connect to with Firefox.

Thank you, Edmeister, for your reply. Just to be absolutely sure, does this mean that after I have formatted my C drive, and reloaded Windows 7 Ultimate and Mozilla Firefox 26, and the Outlook app, I will be able to download all my old emails, contacts, and email addresses? PS: I have forgotten where I downloaded the Outlook app. Can you point me in the right direction?

Outlook has been used with several different products and services:

• Outlook Express (Windows XP)
• Outlook 1997, 2000, XP, 2003, 2007, 2010, 2013 (Microsoft Office)
• Outlook.com (successor to Hotmail and online version of Windows Live Mail)
• Outlook Web Access / Outlook Web App (corporate mail)

The first two are software that may store mail on your computer, the second two are web-based applications that keep your mail on a remote server.

There's a simple way to tell.
Before you proceed with reinstallation of windows do the check:

Try to access your email 'using Firefox', i.e. logging in on a web page of your email, e.g. gmail, fastmail.fm, hotmail.com etc.:
If you see your email -> it's safe! (it's available from your email provider server)
Whatever you do with your disk won't delete it.

it is important for you to not use any email program after doing the check. Badly configured Outlook or other email program (client) may delete your email from your email provider server.

If you just love peace of mind, do the check again JUST BEFORE you proceed with reinstallation of Windows or any stuff that seems dangerous to you.

Good luck!