google-chrome: add Google Chrome based on Chromium
firefox: sessionstore file moved with Firefox 33

It seems the sessionstore file moved in Firefox 33:
http://forums.mozillazine.org/viewtopic.php?f=38&t=2881109
Merge pull request #6 from pstuifzand/google-chrome

google-chrome: add Google Chrome based on Chromium
Merge pull request #7 from pstuifzand/firefox-33

firefox: sessionstore file moved with Firefox 33
a bit of docs