When dealing with percentage widths (and I assume height), certain UAs do the following
This pink container <div> is 1000px wide. There is no reason for rounding here!
This 1004px box represents the body of a maximised browser in a resolution of 1024×768
In 50% of possible browser widths, strict rounding means that the 8 floats with percentages summing 100% have a computed width of > 100%. Win/IE takes this approach and draws 8 floats of 126px, so the last float actually wraps onto the next line, ruining the intended display. Gecko appears to take a ’smart’ approach and draws a mixture of 125px and 126px boxes, so that 100% is indeed 100% - IMHO all browsers should do the same. At the very least, they should play it ’safe’, and draw 8×125px boxes.