How to check if browser is Firefox in CSS

I was reading how to do this,... but have not come up with a good answer for this

the thing is that, in eclipse's internal browser this css loo开发者_Go百科ks weird because of the margin

#tabs {
    margin-top:-50px;
    float:left;
    font-size:100%;
    line-height:10px;
    vertical-align:top;
    }

but in firefox it works fine.. so i am tring to say something like if firefox use margin otherwise do that read the margin-top.. i saw something like this but is not working (and again new to this :) ) thank you for your help

#tabs {
    [if Gecko] margin-top:-50px;   (not working)
    float:left;
    font-size:100%;
    line-height:10px;
    vertical-align:top;
    }

CSS has no way to detect which browser or what engine is used to render the given item. I don't know anything about the eclipse internal browser, but standards compliant browsers should render it all roughly the same. I'd recommend using a CSS Reset to reset all default styling for all elements, which will normalize as much as possible, and go from there.

This isn't possible with CSS alone; you'd have to use a little bit of JavaScript. Providing the Eclipse browser doesn't run JS, you could just do this:

document.getElementById("tabs").style.marginTop = "-50px";

If the Eclipse browser does run JS, you'll have to detect it either by finding the user agent, or doing some functionality testing (I forget what it's called).