I don't think Firefox has any hooks that would prevent the screensaver from starting. Perhaps it can't compatible with newer Firefox version. Please give another screensaver a try.I am using Digital Aquarium Screensaver and it works ok.

I have the same issue with my Mac. If I try to use a Hot Corner to turn on my screensaver, it will turn on for a second or two and then turn off. If I wait for it to turn on after 3 minutes of inactivity, it won't even try. If I shot down Firefox 4, it works just fine. What gives?

I tried a different screensaver and it works. Thanks

Win Tool, I downloaded Firefox screen saver and it never worked, so I downloaded the aquarium one that you suggested and it never shows up either. Do you have any idea why? Thanks, Emilie in NC

I just bought new laptop w/7 home premium, and as soon as I boot up FF, ALL screensavers stop working. I even went so far as to set up new user profile, as instructed by MS. Realized just last night, that the screensaver is working on BOTH profiles when I first sign on...but as soon as I boot up FF, it stops. Any help will be most appreciated, since I love FF and really don't want to have to give it up just so my screensavers will work. Odd thing is -- everything works fine on my wife's 2-year old Windows 7 laptop, but not on my new one.

For what it's worth I've tried a different screensaver with no luck. I also tried restarting in safe mode, but that didn't help either.