Different browsers interpret web site code differently. That’s not remarkable or a revelation . . . it’s been that been that way since Christ designed the first web site in the Netscape days.
Not all browsers are totally wwwc complant (“World Wide Web Consortium” . . . the organization that sets coding standards for web sites). For example, some won’t interpret HTML5 the same way exactly, or certain css codes (“Cascading Style Sheets”) have a different look on different browsers.
Internet Explore used to be particularly cranky about HTML versions and css versions (I haven’t used IE in a while, so I don’t know if it’s still that way.)
I know when I designed a web site I put the logo/comment that the site was best viewed in Firefox. Some sites have a logo/comment that it was designed to be viewed best in . . . Internet Explorer.
So, I’m curious. Do you guys test for different browser renderings, and if so which browsers (AND VERSIONS) do you test?