tips
open new tab on the right side of current tab
http://www.koikikukan.com/archives/2015/04/09-005555.php
1. input "about:config" on the address bar.
2. input "browser.tabs.insertRelatedAfterCurrent" on the search form.
3. change "browser.tabs.insertRelatedAfterCurrent" value into true.
4. save configuration.