Temporary fix for Steam's UGC servers serving WebP images to Firefox users.

steam-image-webp-cache-busting.user.js

// ==UserScript==
// @name Steam Image Fixer
// @description  Forces Steam to regenerate image files because their cache is serving WebP to Firefox users.
// @namespace steam-image-webp-cache-busting
// @match https://steamcommunity.com/*
// @grant none
// @run-at document-start
// ==/UserScript==

let rewrite_image_url = (image) => {
  if (image.src.includes("/ugc/")) {
    let url = new URL(image.src);
    
    if (!url.searchParams.get('shame_valve_for_serving_webp_to_unsupported_browsers')) {
      url.searchParams.set('shame_valve_for_serving_webp_to_unsupported_browsers', '1');
      image.src = url.href;
    }
  }
};

let observer = new MutationObserver((mutations) => {
  mutations.forEach((mutation) => {
    mutation.target.querySelectorAll('img').forEach(rewrite_image_url);
  });
});

observer.observe(document, {
  childList: true,
  subtree : true,
  attributes: true,
  attributeFilter : ['img'],
  attributeOldValue : true
});

document.addEventListener("DOMContentLoaded", (e) => {
  /* fix existing images */
  document.querySelectorAll("img").forEach(rewrite_image_url);

  /* fix thumbnail viewer and prevent extra load because mutation handles this too late */
  if (typeof rgScreenshotURLs !== 'undefined') {
    Object.keys(rgScreenshotURLs).map((key, index) => {
      if (!rgScreenshotURLs[key]) {
        return rgScreenshotURLs[key];
      }

      let url = new URL(rgScreenshotURLs[key]);

      if (!url.searchParams.get('shame_valve_for_serving_webp_to_unsupported_browsers')) {
        url.searchParams.set('shame_valve_for_serving_webp_to_unsupported_browsers', '1');
        rgScreenshotURLs[key] = url.href;
      }
    });
  }
});