I have noticed this behavior with a localStorage full (5MB of packed strings) but it doesn't freeze, it just takes an awful lot of time rendering those weird strings. If you look at your task manager (or a top in a terminal) while trying to open the dev tools, you'll notice that one full core is crunching data for Chrome. This is the rendering part. while the rendering is done you can interact with your dev tools again.
Firebug exibits the same behavior
This has to do (I think) with the handling of ultra-long strings coupled with the rendering of obscure UTF16 characters. With just a few kilobytes in localStorage everything is instantenuous.
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