How hard would it be to put in a confirmation box for closing tabs / windows? I have lost track of how many times i have inadvertanly closed one. Then have to recall what was filtered to that particualar tab when i restore it.
You can uncheck the "ESC to close" option on each window, which will cut down on accidental closings.
That only helps if a) someone is comfortable editing the UI and b) if they NEVER want to close that window/tab/etc. Having an option 'Closeable' in the options would be nice.