I reinstalled FF 3.6 and will try to remember to wait at least two months before installing an update, until the mozillas have figured out their ware. Don't install FF4 on Fedora 9 or older.

Helps to read the system requirements page before installing a new version of any software before installing it on an old Operating System like Linpus.
http://www.mozilla.com/en-US/firefox/4.0/system-requirements/

Of course, the fault lies with Acer for selling new netbooks with 3 1/2 year old operating systems that aren't supported too good. I ran into the same thing with an Asus EeePC that I got in 2009, I could install Firefox 3.0 which was already 4 months old at the time I bought that netbook.