Different browsers render pages differently. Take for instance this
template. Look at in firefox and then look at it in internet explorer? How many differences can you find. Hint... drop shadows, rounded corners and bevel text. To fix the differences on that template, I would need to create images as the reason IE does not display the rounded corners etc it because they are all created using CSS3 that IE does not support.
In this case it does not matter in my opinion as they just enhance the design, but are not critical as in the page is still 100% functional in IE.
In your case you need to look at what the differences are, if they are critical, changing your browser is not enough, you will need to fix them or change your theme.
If you post a link to the webpage, we may be able to give you more specific advice.