Great that you are running the installer in graphic mode (LXDE)
I'm afraid iceweasle needs more RAM than what is available. But
- can you install?
- can you edit partitions with gparted?
- can you read the pdf files?
- can you install some utitilty for example scrot (and take screenshots)?
Edit: htop is installed. Can you run it in a window and check the CPU and RAM usage while doing other tasks? Or is it too close to the limit?
apt-get install scrot
And I think you can at least install in text mode (using the command line with mkusb, that is prompted).