clarify the global scope

* prefix |window| to the global property
  RULES;
  1. do not prefix to built-in objects that has nothing to do with
  |window| context (e.g. |parseInt|, |Date|)
  cf. http://www.herongyang.com/JavaScript/Built-In-Object-Global-Properties-and-Functions.html
  2. prefix to properties that are particular kind of |window| context
  (e.g. |window.document|, |window.top|)
  3. prefix to properties that is exposed by JS code (e.g.
  |window.makeURI| of Fx code, |window.ucjsUtil| of a user code)
  4. I'm omitting prefix to |gBrowser| for readability

* ensure |undefined| constant and do |value === undefined|
update comments/formats
rename function
simplify |createNode|
use |window.content| for readability
improve error throw
improve |convertForUI()| and rename to |toStringForUI()|
remove useless function
remove useless code
update comments/formats
remove useless parameter
update comments/formats
rewrite |toggleUnreadTab| and rename to |setStateForUnreadTab|
make reference of |gURLbar|
make reference of |gFindBar|
move exposed object to end
make function |toggleShowOverLink|
enclose CSS setting function
implement showing visit time of link
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