I use both.  But I find Firefox to be far less stable than Chrome.  I’m also not sold on the memory improvements.  They’ve separated the plugins (plugin-container.exe) from the browser (firefox.exe) which is good, but you have to remember to tally up both in order to get an accurate picture.  For me, that picture sometimes exceeds 2gb of RAM.  It’s harder to tabulate Chrome’s memory usage, but even if it is rather high, it doesn’t routinely slow down the whole computer.