The thing is, if it is just style changes, it is better to be done via Stylish. Extensions, for most of them in chrom(e|ium), would would absolve resources in the system via a separate process. For computers with less memory, running multiple chrome extensions would not be a good idea. Better to run extensions that benefit all sites than just one.
Also as a side note for using that in Firefox 3.6 , it seems that submit button's orange background is not applied like in chrome, so it would be harder to read the text on the button. Someone with Firefox 4 on hand may to see check on that as well.