Last week, I visited my friend and borrowed his PC to to surf the net for a while. Each time, when I launched the Firefox browser in his computer, two homepages coming out. So, I asked him why.

Here is the answer he gave.
To set multiple homepages for your Firefox browser, go to Tool >> Option.
Under the Main tab, there is Home Page location box for you to set your homepage.
To have multiple homepages for your Firefox browser, enter the homepage url separated by a pipe symbol and so on like this picture below. Click OK.

Restart your Firefox browser and you will see that multiple sites open in separate tabs as your homepages.