Hi, about your big icons, I'm not sure what is your big. But if it's really that big, you might want to edit the file XF86Config-4 (/etc/X11/XF86Config-4) as a root. Then find this section:
Section "Screen"
Identifier "Default Screen"
Device "Generic Video Card"
Monitor "Generic Monitor"
DefaultDepth 24
SubSection "Display"
Depth 1
Modes "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 4
Modes "1024x768" "800x600" "640x480"
...
EndSection
The list is pretty long. Now you should add (not replace) into the line Modes "...." "...." "...." the resolution that you usually use. For example, my config (above) will result in 1024x768 screen resolution (of course if my graphic card supports it

). Edit all the line Modes, but most importantly the subsection with highest Depth value. After you save it, restart X.
For firefox, you can (as harken pointed out) download the file from mozilla website or use apt-get to install the package mozilla-firefox:
# apt-get update
# apt-get install mozilla-firefox
This will install all the dependancy altogether (that's y I love apt)