[Linux] Set as random the Firefox browser homepage.

First of all put a list of selected urls (one per line) in a file called urls.txt and save it in ~/.mozilla/firefox/*.default/urls.txt. Then put the follow code at the very begin of /usr/lib/firefox/firefox.sh (just below of the "shabang" #!/bin/sh):

ddrs=$(shuf-n1~/.mozilla/firefox/*.default/urls.txt)
nwli="user_pref(\"browser.startup.homepage\","$ddrs");"
sed-i"/browser.startup.homepage/c\\$nwli"~/.mozilla/firefox/*.default/prefs.js