[TxMt] feature request: arrow-left to go to parent item in hierarchical list views?

[M Spreij]

The Thunderbird mail client and Mozilla's bookmark editor both have a 
neat feature when you're cursoring through hierarchical lists (threaded 
view in Thunderbird): when an item is selected and you hit the 
left-arrow (or arrow-left?) key, it jumps to the parent item. Hit it 
again and the parent item closes. The latter already happens in a lot of 
places, would be nice if the former behaviour was put in as well :-)

/MS