I guess the only conclusion for this is that Fx4 runs with varying degrees of success on different computers. I'm using it right now, very happy with it. It doesn't mess up any of my embedded flash bits or Youtube movies anymore, which Chrome did. I prefer it now, but I'm still getting used to everything under the hood. You can also make Fx4 as streamlined as Chrome with the toolbar editor. The only difference from my copy of Chrome and Firefox is that I have my bookmarks on the toolbar.
So you understand where I'm coming from: my desktop here has every major web browser installed. No reason, just to have. Checking compatibility with sites.