jquery - jQuery and conditional logic- alter html BEFORE using show() or after?

Question

I'm using jQuery to do some browser version checks to customize my HTML content.

My first check is simply (pseudocode)

if browser is IE or browser is Firefox
show div1 and hide div2
else
hide div1 and show div2

Simple enough. But in addition if I am showing div2 I want to perform the additional check

if (OS == Mac and browser version less than 4 (firefox 3 or less on Mac)) OR (is IE less than 9)
do foo(alter div2)
else
do fud(leave div2 as is)

My question is should I be doing the 2nd conditional check first, BEFORE I show the div?