Would work great if not for bug Rated 4 out of 5 stars
It works, but there is a problem.
Currently the extension will only work if both the drop down "A" button and drop down "P" button are displayed in the toolbar.
This is because the code tries to read attributes for the button and will throw an error if the button isn't in the toolbar. The fix is simple. In overlay.js check to make sure that document.getElementById("fullZoomBtn_popup2") and document.getElementById("textZoomBtn_popup2") are not null (in line 62) before reading their state.
Once that is fixed, the extension works great.
I would have emailed the author directory, but there is no email address on the support site.