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Just to add some data to this:

Today I noticed high RAM usage.  I had 1176 nodes and saw Tabs Outliner is using 767 Megs of RAM.  I un-enabled and then re-enabled the extension and re-opened the TO window, and now I see 44 Megs of RAM used.  My system has 16 gigs.

I rarely restart Chrome, but lately I've been restarting TO about once a week due to this.