This trick will help you get a multiple homepage on your firefox browser. Like if you want to set Google, Facebook and Youtube as your homepage than follow the tutorial below:
1.Go to Tools>Options>General
2.In the "When Firefox starts:" drop down menu, select as "Show my home page".
3.In Home page give your homepages separated by a | (pipe symbol).
Now next time when you start Firefox all of your three home pages will be displayed simultaneously.