it's hard to determine how this sig would look in FF(i'm currently stuck with IE). but i would have to say it looks pretty good, you did a great job rendering Homer, i can't really see any flaws with him currently. the only two complaints/suggestions that i really have for you are:
1. if you are using photoshop, make sure that you change the text mode from "none"(i believe that is what the option is called, it's whichever one is on the top of the drop down boxe's list), to the second option on that drop-down box. i do believe that the second option is "crisp", setting it to this text mode should eliminate all of the aliasing that you can see going on with the text here.(it's really noticable in the stroke).
2. i would also make sure that when using a png for transparency, you never have any run-off. by run-off i mean make sure that none of the image goes outside of the image's boundaries, i can see right now, that the reflection reflects off the images dimensions. fixing this problem would involve selecting the reflection layer, and taking the eraser tool(shortcut key "E"), with a soft brush on size ~30, and just do a quick run near the bottom of the document. so that it "fades away" before reaching the bottom of the image. in my opinion, you could also lower the opacity on the reflection's layer, since it would normally take quite the refective surface to produce that strong of a mirrored image to be seen.
sorry for the long post, i've been finding myself posting posts alot longer lately for some reason
i hope i helped a little bit.