I don't use lxde (KDE for me
) but I extract the Firefox download to a new folder in /home and run the firefox
file from there.
I usually create a new menu entry for it and also drop an icon onto the panel and run it with the firefox -P
command so I can choose which profile to use.
That works fine for me (and leaves my original Firefox 3.6.12 as is so I can use it when I want)
Not sure how this will apply in lxde though.........