Here I explain how to easily install an ad blocker for Steam’s built-in web browser.
The process is very simple and doesn’t require any file modifications or other hacks.
It simply involves going through the browser’s options, which are normally not accessible, but a simple trick makes them available.

Carefully follow the steps below :

Here's how :

1. Right‑click on an element of the main Steam Store page. For example, on a game.
   Then click on "Open the link in a new tab"
   
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2. A window will then open.
   Select the address in the URL bar and replace the URL by this and press enter :
   
   chrome://extensions/
   
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3. Another window will open.
   This is the Extensions settings page of the integrated browser (based on Chromium).
   
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4. Now click on the Chrome Web Store link on the left to reach the Extensions store.

1. Once the Store page is open, click on the search bar, type the name of the ad blocker you want. Here as example, i'll pick AdGuard.
   Select it, then click on Add to Chrome, then Add the extension, to install it.
   
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2. A window will open asking you to save the extension to your computer.
   Choose the desktop and click on Save.
   
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   There you go, the extension is now installed !

If you chose AdGuard, here’s how to configure it to optimize its use :

• After installing the extension, this window will open.
  Configure it as shown in the images below.
  
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• Enable everything except Annoyances (this may simply block your access to certain websites).
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• Whitelist the following two Steam links (just in case).
  
  https://steamproxy.com/steamstore/ https://steamproxy.com/
  
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• Disable everything here :
  

As you can now see, the extension is properly installed 👍
You can now close the different windows (Store and Extensions).

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You can now enjoy smooth browsing without advertising clutter (or at least greatly reduced) in the browser while you are in-game.
YouTube ads are also blocked. However, there is a small delay before the video starts.
This is a known method implemented by Google to inconvenience users of ad blockers.
Boo-hoo 👎 !
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