I've tried tree style tabs a few times but it always ends up being too much. The implementations of vertical tabs I've liked best so far are OmniWeb's (perhaps

I've tried tree style tabs a few times but it always ends up being too much. The implementations of vertical tabs I've liked best so far are OmniWeb's (perhaps one of the original vertical tab browsers), Edge's, and Firefox with Tab Center Redux and custom CSS to hide Firefox's frustrating mandatory sidebar header.