Does this occur other times that you navigate to your home page, such as:

• Opening a new window (Ctrl+n)
• Clicking the Home button or pressing Alt+Home on the keyboard

If so, there might be an extra vertical bar character toward the end of your home page setting. You can check that in the Options dialog:

orange Firefox button (or Tools menu) > Options > General

More info on that:

• Startup, home page, tabs, and download settings
• How to set the home page

If not, it's possible that there's something odd in the shortcut you use to start Firefox. You can check here:

right-click the icon > Properties > Shortcut tab

The target field should have this, no more, no less:

"C:\Program Files (x86)\Mozilla Firefox\firefox.exe"

By the way, does the blank tab have anything in the address bar, or just "Search or Enter address"?