In the `zoom{In, Out}` functions in `PDFViewerApplication`, we prevent the zoom value from becoming smaller/larger than `MIN_SCALE/MAX_SCALE`.
However, if the user sets the zoom level through the hash parameter the zoom buttons might not be correctly disabled; try http://mozilla.github.io/pdf.js/web/viewer.html#zoom=10.
Note that this issue has been present since "forever", but given that the solution is so simple I think that we should just fix this. (I'm also fixing a stupid typo I previously made in the JSDoc comment.)