I've only done this with IceCat but. One quick fix I figured out is to open
your about:home, then ctrl+S the page as xhtml. Once you've done that you
could save that to Templates or something, then open it within the browser,
and right click then hit view page source. You should then find this line
with DDG,
Pic#1
and change it to this(I used Ixquick, you can use whatever you want).
Pic#2
When you're done open preferences and change about:home to
/home/Templates/IceCat Start Page.xhtml. You'll now have that address in the
URL bar, instead of empty space, but It's worked well enough for me for the
time being.
