The problem is caused by the Imagus extension, which during its animations generates ‘mousedown’ events for the right mouse button. This causes Zoom Page WE to think that the right mouse button has been pressed by the user. The proper fix would be for Imagus not to generate ‘mousedown’ events.

The workaround is to un-tick the “Enable mouse Right+Wheel to zoom in/out” option in Zoom Page WE Options.