After selecting for example the zoom level "page fit", if would be intuitive and desirable to be able to navigate the document using the arrow keys. Right now pressing an arrow key (even and especially left/right) changes the zoom level, although you just selected the desirable zoom level manually.

EDIT: the same thing holds for the page up and page down keys.

/**
 * @typedef {Object} ToolbarOptions
 * @property {HTMLDivElement} container - Container for the secondary toolbar.
 * @property {HTMLSpanElement} numPages - Label that contains number of pages.
 * @property {HTMLInputElement} pageNumber - Control for display and user input
 *   of the current page number.
 * @property {HTMLSpanElement} scaleSelectContainer - Container where scale
 *   controls are placed. The width is adjusted on UI initialization.
 * @property {HTMLSelectElement} scaleSelect - Scale selection control.
 * @property {HTMLOptionElement} customScaleOption - The item used to display
 *   a non-predefined scale.
 * @property {HTMLButtonElement} previous - Button to go to the previous page.
 * @property {HTMLButtonElement} next - Button to go to the next page.
 * @property {HTMLButtonElement} zoomIn - Button to zoom in the pages.
 * @property {HTMLButtonElement} zoomOut - Button to zoom out the pages.
 * @property {HTMLButtonElement} viewFind - Button to open find bar.
 * @property {HTMLButtonElement} openFile - Button to open a new document.
 * @property {HTMLButtonElement} presentationModeButton - Button to switch to
 *   presentation mode.
 * @property {HTMLButtonElement} download - Button to download the document.
 * @property {HTMLAElement} viewBookmark - Element to link current url of
 *   the page view.
 */
class Toolbar {
  /**
   * @param {ToolbarOptions} options
   * @param {EventBus} eventBus
   * @param {IL10n} l10n - Localization service.
   */
  constructor(options, eventBus, l10n) {