TabHandler: minor fixup

* update comment
* fix wrong filename of |log|
FindAgainScroller: ensure showing selection at blinks canceled
FindAgainScroller: blink a normal selection instead of attention
FindagainScroller: minor fixup

* update comments
* clean up empty lines
* arrange local variables
implement timer handler with |nsITimer|

* replaces the native timers that are used frequently or repeatedly with it
* moves the declaration of the imported functions to the top of a script
FindAgainScroller: reset values associated timers