I hate to be one of those "it depends" guys, but in this scenario it actually does depend on what you're saying looks different. From a technical behind-the-scenes "code" perspective, browsers have different (often optimize-able) standards, or lack of standards, from everything to font-sizes all the way up to default colors of various things (fonts, div's, etc.). Often times different browsers follow particular rules when other browsers do not - Even when it comes to how a website's layout is spaced. For example - My new studio website that I am working on. I had to do A LOT to the code in order for it to adjust to all the little quirks that make Firefox one of my least favorite browsers. Whereas in Safari, Opera, and even Omniweb it looked/looks flawless. Although it does look normal, to this day, it still won't work EXACTLY how I need it to in Firefox without messing up all of the other browsers presentations that I have tested. It is a very tricky, sneaky, and overall tedious thing. Anyway, I hope this message makes sense and/or helps you in some way!
If your website use submit buttons, radio button, check box etc. all of them visualized depending on the visitors operating system & its style. Display resoluation is affecting quite a lot the way is web site display. Web browser do not render page pixel by pixel.
Uhm, could someone translate that into English for me? Jokes aside, without seeing the site in question (or understanding the question, that was a question, right?) nobody's going to be able to give you a concrete answer. Are you saying that it changes appearance every time you close/open the browser, or are you saying that all the different browsers show a different appearance. The first shouldn't happen, the second probably means invalid markup, poor methodology, outdated coding techniques, and a whole host of other issues. But without a URL, we're shooting blind.