Uncomment the bottom half (i.e. remove /* and */) and change 69px to whatever your heart wants. The way this works is 2 seconds after the page begins to load it will insert a rule into the stylesheet to override the emoji's maximum height.

// ==UserScript==
// @name        New script hexbear.net
// @namespace   Violentmonkey Scripts
// @match       https://live.hexbear.net/c/movies*
// @grant       none
// @version     1.0
// @author      -
// @description 3/1/2024, 10:31:12 PM
// ==/UserScript==
(function() {
    'use strict';
      document.getElementById("chatwrap").style.paddingLeft="1px";
      document.getElementById("chatwrap").style.paddingRight="1px";
      document.getElementById("videowrap").style.paddingLeft="1px";
      document.getElementById("videowrap").style.paddingRight="1px";

      // Optional set custom emoji size.
      // Uncomment the lines below and change emojiHeight from the default 69px to whatever number you want.
      /*
      const emojiHeight = "69px";
      $(document).ready(function() {
        setTimeout(function() {
          for (const sheet of document.styleSheets) {
            // This is, as generically as I can tell, the correct css ruleset.
            // sheet.href has to be of local origin.
            if (sheet.href === null && sheet.cssRules.length > 1) {
              sheet.insertRule("#messagebuffer img { max-height: "+emojiHeight+";}", sheet.cssRules.length-1);
            }
          }
        }, 2000)
      });
      */
})();