I don't see a problem pointing out issues with Firefox. To me this is helpful compliance testing. I'm sure the Firefox guys will get on it and all browsers will approach "the standard."

Yes. Like another commenter in the IE10 preview thread pointed out: the issue will be fixed in FF4 long before IE10 is released.

Won't it break the sites that worked around the bug?

It depends on how you do it, what bug it is etc.

For instance.. IE6 had a difference in the way it adds margins and widths for a long time - it's a bug (at least a deviation from the standards), some people relied on it.. but the common workaround is to not assign margins to the same elements as you added widths on. (and there are other methods, like display:inline coupled with floating..etc)

The point being.. that workaround doesn't break on newer versions - it simply avoids stepping on those stones.

>If I noticed a lot of differences I would assume it to be IE’s problem right off the bat.

That sounds like a problem with you if you assume so without investigating first. Do you think Firefox is infallible?