Rewrite tooltips:
* use own <tooltip>
* generate tooltip on popupshowing (and show actual elapsed time)
* show closed time in button tooltip
Group tooltip-related functions
Add separate template for button tooltip
Use gray color for additional data in button tooltip
Don't break button icon in Firefox 2
(nsIStyleSheetService doesn't work as expected)
Restore tooltips in tab context menu ("showInTabContextMenu" option)
Add constant for id of menu in tab context
Middle-click on menu in tab context to restore last closed tab