Some of the websites are designed to work only for Internet Explorer, especially some of the government and university sites. These sites are used for filling up of online application forms of various kinds. But if you are a Firefox user and do not feel comfortable outside your Firefox world, then you can use Internet Explorer inside a Firefox tab using the free IE Tab v2 add-on.
You can install the IE Tab v2 add-on from the Mozilla add-ons website. The installation of this add-on requires you to restart the web browser and it can be used immediately after the restart. After the restart, you would see a Firefox icon in the add-ons bar on the right side. Clicking on this icon would switch the current website opened in the current tab to the Internet Explorer tab. This would also change the icon in the add-ons bar to Internet Explorer.
If you want to open a link in the Internet Explorer tab, then you can right-click on that link and choose Open Link in IE Tab. If you want to open the link in the Internet Explorer web browser, then you can right-click on it and select Open Link Ext. App.. This would launch the Internet Explorer and open that link in it.
In the IE Tab add-on options, you can add websites to Sites Filter list. All the websites in this list would always be opened in the Internet Explorer tab. You can also change the context-menu entries, external application (by default, Internet Explorer), and the IE compatibility mode. IE Tab supports four compatibility modes.
So if you want to quickly view a webpage in the Internet Explorer browser, then you can use the IE Tab v2 add-on. This is really useful if you want to test a webpage in Internet Explorer, or if the site is not working in Firefox because it was specifically designed for the Internet Explorer.
You can download and install the IE Tab v2 add-on from https://addons.mozilla.org/.