Instal and run Firefoxportable from Flash Drive

Hi,
I am using XP SP2 and downloaded Portable Apps Suite v 1.1.0.0. to Downloads file on D drive.
1) Ran setup and installed Suite in Program Files on D Drive.
2) Clicked on Start PortableApps, clicked on PortableApps then copied SudokuPortable folder to Flash Drive.
3)Opened Sudoku on flash drive and all OK.
4) Then Copied FirefoxPortable folder to flash drive and tried to open. Microsoft reports,
"Firefox has encountered a problem and needs to close"
5)Tried to open FirefoxPortable from D Drive and all OK.
6)Flash drive is 512Mb so is this too small to allow FirefoxPortable to run or have I used the wrong installation procedure. I note in forum from 'lefthome' that similar problem occurred but there was some confusion about size needed to run application.
Regards, Dave