Fix bug #4593 (HTML menus / context menus are too narrow: keyboard shortcut
wraps to second line in some places) -- see notes in bug for the sordid
details...
In-browser polish:
- remove Cut/Copy/Paste menu items since they can't be made to work
- remove Check for Update menu item which makse no sense in this context
- fix bug where Extension Manager lists all default extensions as user
extensions (with broken Remove button)
- update message shown when index.html opened directly via file://