Greasemonkey script to fix slow Figma mouse wheel scrolling in Firefox on Linux

figma-mouse-wheel.user.js

// ==UserScript==
// @name      Figma Mouse Wheel Speed Fix
// @namespace https://adam.nels.onl
// @match     https://www.figma.com/*
// @grant     none
// ==/UserScript==

// Mouse wheel scrolling in Figma on Firefox + Linux is unbearably slow.
//
// This script catches all mouse wheel events on the main canvas,
// then re-fires them with the deltaX/deltaY increased by a multiplier.
//
// - Adam Nelson <adam@nels.onl>

const MULTIPLIER_X = 30;
const MULTIPLIER_Y = 10;

function speedUp(ev) {
  if (!ev.isTrusted) return true; // Prevent recursion.
  
  const { clientX, clientY, screenX, screenY, shiftKey, ctrlKey, altKey } = ev;
  const newEv = new WheelEvent('wheel', {
    bubbles: true,
    cancelable: true,
    view: window,
    clientX,
    clientY,
    screenX,
    screenY,
    ctrlKey,
    shiftKey,
    altKey,
    deltaX: ev.deltaX * MULTIPLIER_X,
    deltaY: ev.deltaY * MULTIPLIER_Y
  });
  
  ev.preventDefault();
  ev.stopPropagation();
  ev.target.dispatchEvent(newEv);
  return false;
}

// Wait for the main canvas to show up.
function addCanvasEvent() {
  const canvas = document.querySelector('.view > canvas');
  if (canvas != null) canvas.addEventListener('wheel', speedUp);
  else setTimeout(addCanvasEvent, 500);
}
addCanvasEvent();