[petera]

I really doubt it would become a one-click privacy measure: If you like to participate in an onion-routed, privacy enhancing, anonymity network, why put it in an browser?

A browser accesses that network, it is the weakest and least point in that setup.

Because tor has no gui? Use vidalia (see https://www.torproject.org/projects/vidalia.html.en).

There are so many ways to track an individual, independent of the network, with java-script, extensions, addons, plugins, client-side-caching that even if tor becomes a feature in firefox, the slightest unmitigated problem, even your behavior may compromise your privacy.

[chakalakasp]

Presumably Firefox would disable all add-ons, Flash, and possibly JavaScript if tor were enabled. Otherwise, yeah, all bets are off.

[petera]

Your forgot to purge the disk- and memory-caches.