Be careful with old versions!
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Fixed issue where the button would sometimes disappear, but reappear when the extension was reinstalled -- for example, this would happen when switching FF versions.
The button WILL disappear from your toolbar as a result of this update; find it in the "customize" dialog and put it back where you want it. This is a consequence of fixing the previously mentioned issue, which is why I've been putting off fixing it. Sorry for the inconvenience.
Target App max version updated to 2.0.0.* on 9/27