Firefox portable

i recently downloaded firefox portable for my 1gb flash drive so i can use it at my local library and it runs real slow and alot of times it stops responding and other times it makes the computer freeze and i just want to know how i can fix it. the computers at my local library are dell computers and have windows xp

It is working on the flash drive, or you installed it onto the library computer.

Have you tried doing 'general surfing' using the browser on the PC to see if it isn't something with the PC?
If it's a PC at a library, you don't really know 'where it's been' and 'what it's been doing'
I have it on my flash drive and it seems to work well-on my PC (I never officially tried it on another PC yet).
Do yourself a favor and install this on your flash drive if you use a public PC,
http://portableapps.com/apps/utilities/clamwin_portable ;)

you need your usb drive to be able to transfer at a fast enough rate.
look here for some speed times (http://usbspeed.nirsoft.net/) or here to run your own (http://www.nirsoft.net/utils/usb_devices_view.html)

I used to run it off a cheap usb drive I had and found it unbearable to use then I bought a higher quality drive and it worked a treat.

same thing for most portable apps I tried

USB flash drives run at many different speeds... speed is often related to the price you paid (though not always).
Flash drives are rated in read performance, Write and sequential write performance, Delete performance... sometimes shown as time to copy from, time to copy to, time to ready from... and operations per minute.
A good and fast flash drive can run at 30 times faster or more operations per minute than a slow one...
Usually the drives are rated also on their long term reliability.
Most of these are related to costs per operation, but not always.