Techpwn has a nice little tip about how you can stop websites from resizing Firefox browser window.

To stop your Firefox Browser Window from resizing you need to:

1. Open Firefox
2. In Windows click on Tools then Options. On a Mac click on Preferences.
3. Click on the Content Tab
4. Click on Advanced button which can be found to the right of Enable Javascript checkbox.
5. Uncheck Move or Resize Existing Windows

Viola! Firefox window now shouldn’t resize automatically on particular websites.

Thanks Techpwn for the nice tip!