Hide any element on the page by meta+alt clicking it. Return the page to normal by shift+meta+alt clicking. https://gist.github.com/bschlenk/a9b19645d6611705b26eb93e3c0288ac/raw/hideit.user.js

hideit.user.js

// ==UserScript==
// @name         HideIt
// @namespace    http://tampermonkey.net/
// @version      1.1.2
// @description  Hide any element on the page, with the ability to restore all.
// @author       Brian Schlenker <bschlenk@umich.edu>
// @match        *://*/*
// @noframes
// ==/UserScript==

(function() {
    'use strict';

    const DISPLAY_ATTR = 'data-display';
    const HIDDEN_ELEMENTS = [];

    function getModifierState(e) {
        if (Object.prototype.hasOwnProperty.call(e, 'getModifierState')) {
            const alt = e.getModifierState('Alt');
            const meta = e.getModifierState('Meta');
            const shift = e.getModifierState('Shift');
            return { alt, meta, shift };
        }
        const {
            altKey: alt,
            metaKey: meta,
            shiftKey: shift,
        } = e;
        return { alt, meta, shift };
    }

    function hideElement(e) {
        e.setAttribute(DISPLAY_ATTR, e.style.display);
        e.style.display = 'none';
        HIDDEN_ELEMENTS.push(e);
    }

    function showElement(e) {
        const display = e.getAttribute(DISPLAY_ATTR);
        e.style.display = display;
        e.removeAttribute(DISPLAY_ATTR);
    }

    document.addEventListener('click', (e) => {
        const { alt, meta, shift } = getModifierState(e);
        if (alt && meta) {
            e.preventDefault();
            e.stopPropagation();

            if (shift) {
                HIDDEN_ELEMENTS.forEach(showElement);
                HIDDEN_ELEMENTS.length = 0;
            } else {
                hideElement(e.target);
            }
        }
    }, true); // use capture to prevent hide-it click triggering other events
})();