I am up to date on all browsers, although the difference is small I can see it quite clearly. The border is just that little bit fuzzier on the corners. But there again we can go into monitor settings graphics cards and so on. I am glad it look fine in all browsers to you and hopefully others too!
Using a 2007 HP laptop 12808x800 resolution if that helps. 15 inch display on it and yes I have put sites together on this and thought all looked just fine then looked on my desktop monitor and it didnt. Of possible interest to you, though, I have a Samsung Galaxy Note 2 phone and also an Asus TF201 Transformer Prime tablet/dock. I use FF on both of them by default because FF seems to get on with anything better than the built in browsers on either device. When looking at sites using them, they dont look any better/worse. It is only when using higher resolution monitors things look different but here's the catch - I find that most people, these days, sacrifice resolution for ease of use. In other words more people seem happy to use their phone or tablet or average priced laptop than worrying about a desktop machine to look at a site. Maybe the business owners are different but their clients seem to be happier not to use desktops for all their online needs these days.
However, for my own peace of mind, I do check on the higher resolution desktop and try to avoid completely things that will cause problems such as you are experiencing. There is always another aesthetically pleasing way to do something that works on any resolution display.
Greg.