disabling Torbutton breaks the Add-ons manager

To reproduce, disable Torbutton and restart the browser. Then go to menu and click Add-ons. This error will show up:

XML Parsing Error: undefined entity Location: about:addons Line Number 359, Column 15:

          <button class="button-plugin-disable"

--------------^

So I cannot re-enable Torbutton from the browser

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