Ubuntu Boot selection is missing in boot loader

I have 4 operating Systems on my computer,

Xp
Vista
7
Ubuntu

The last time I've booted to Vista and 7 was probly a month or so ago, so they aren't the problem. I Always boot to XP though. I boot to Ubuntu for office work because I like the look and feel of it better.

Here's the problem.

My Mozilla Firefox broke on my WIndows XP, so i did a system restore. When I did this, Ubuntu's boot selection was gone on the boot loader. I'm guessing I restored to a time when Ubuntu wasn't on the boot screen.

How can I get Ubuntu on my boot screen again. I can't do a system restore back to the time it was working, or else Mozilla won't work on my XP.