Rated 3 out of 5 stars

Do this at your own risk, and backup your data first.
1. xpi files are simply zipped packages usually containing an install manifest file and a java .jar code file.
2. Mozilla installation examines the install file. Open it from winzip, find the ... line and update it.
3. Take a deep breath and see if it still works. Fortunately, Java just ignores anything that's nonsense, so even if it doesn't work, it probably won't do any harm.