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The only method I am aware of would be to detect an addition to the useragent some addons make. Not all addons add a signature to the useragent so unless there is another way beyond that you've lost me there.
Toolbars such as Hotbar do leave a signature in the UA so you could for example do this...
if (navigator.userAgent.indexOf("Hotbar")!=-1)
{}
The only reason I'd personally use anything to detect toolbars is to let the user know their computer is probally infested from being uninformed victim of internet exploiter.