Again, another complicated process. First, you'll want to visit the VEXcode V5 site. Next, open up DevTools, go to Sources, and find the file that starts with main.bundle.js?v=.
Within this file, you'll find all sorts of gems (such as how to communicate with the V5 Brain over serial, etc). You'll want to Ctrl+F for VEXOS_V5, which'll take you to a function called getCurrentFirmwareVersion(). This is similar to the SDK, where you first get the catalog.txt file to get the most recent version, then download it with a certain prefix.
Visit the URL, and you'll be greeted with the current version number (similar to the SDK).
Use this version number, and replace the URL containing catalog.txt with it, like so:
https://${URL_WITH_NO_CATALOG.TXT}/${VERSION_NUMBER}.vexos
Visit this site, and your browser will download a file ending in a .vexos extension. This is just another .zip file renamed, so
use your favorite ZIP tools to extract it's contents.
Congratulations! You just grabbed the most recent firmware version for the VEX V5 Brain.