Accessing your email account in a Web browser, such as Firefox, is usually easy-peasy, as long as you use a Web mail provider, such as Gmail, Outlook.com or Yahoo mail. Simply enter the name of the website such as "gmail.com" or "outlook.com" into your browser's address bar, and then sign in with your email username and password. If your email account is on an Exchange server, which is often the case at universities and large companies, you can only access your email with Firefox using the Outlook Web app. Not all organizations provide support for the Web app; Check with your school or employer to see if it can provide you with a link for access.
You can also set up Firefox to open your preferred email program for sending messages whenever you click an email link on a Web page. Select your default email app from the Applications tab in Firefox's settings: Find the "mailto" entry in the column, and then select your preferred email app from the drop-down list.
Not on the List?
For most Web-based email apps, such as Gmail, you must first install a Firefox plugin before the app will show up on the list. To find a list of these types of apps, go to Firefox's Add-ons page, search for "mailto" and the name of your email provider, and then install one of the "Notifier" plugins that appear in the results. For example, installing the Gmail Notifier plugin adds Gmail to Firefox's list of available email apps. In the case of desktop email clients, such as Microsoft Outlook or Mozilla Thunderbird, you may need to set the app as your default Windows email app before it will appear in the Firefox list.