Firefox starting three different ways!

I have a problem I have no idea how to begin to fix. I installed Firefox Portable 3.0.4 five days ago after I transferred all files on my USB to an external drive. This was because my old Firefox 3.0 which would run very reliably from a USB stick suddenly stopped working on Vista on my laptop. (Vista also crashed my USB stick regularly but that was a problem caused by other software on the stick) In an effort to correct this I installed a new (3.0.4) version of Firefox Portable and copied all files in the Data/profile directory across to the new version. The new version also did not get past the initial flash screen on Vista but worked perfectly on my old home desktop running an early version of Win XP. (Service pack 3, I think) However, from my work computer also running Win XP an empty shell of Firefox Portable opens, but does not respond to anything except that it appears to have a live menu bar. (and yes, I changed the proxies). I checked the error console and got 2 error notifications
First error

{Exception..."Component returned failure code: 0x80570016 (NS_ERROR_XPC_GS_RETURNED_FAILURE)[nsIJCSID.getService]" nsresult: "0x80570016 (NS_ERROR_XPC_GS_RETURNED_FAILURE)" location: "JS frame:: file:///Q:/Julia%20Mobile%20Data/Program%20Files/Firefox%20Portable%203.... :: bg_initPlaces :: line 389" data:no]

file:///Q:/Julia%20Mobile%20Data/Program%20Files/Firefox%20Portable%203.... Line 389

Second error
uncaught exception [Exception... "Component returned failure code:0x800700e (NS_ERROR_OUT_OF_MEMORY)[nsIDocShellHistory.useGlobalHistory]" nsresult:"0x800700e (NS_ERROR_OUT_OF_MEMORY" location:"JS frame::chrome://browser/content/browser.js :: prepareForStartup ::line 759" data:no]

Can anyone unravel this mystery?
Julia T