nonspecialist

I've been using uBlock Origin for ... years, apparently ... and this is the first time I've actually specifically used the element filter capability. It was initially simple, then it didn't work, then I had to go into the details of the syntax so I could deal with the “Office on the web” pages whose design prevents the use of the simple element picker.

Just a couple of caveats first:

• This won't work on the native applications (eg if you run Outlook in Windows or Mac instead of using the web interface)
• This was tested on my setup which includes Firefox and Chromium, and is on Linux; it should work on other systems, but I don't have others to test on.

uBlock Origin (Firefox et. al.)

NOTE: for Chrome/Chromium based browsers, see uBlock Origin Lite below.

1. Open the uBlock Origin preferences page. You've got a few ways to do this:
   • click the “Extensions” browser toolbar icon (looks like a jigsaw puzzle piece) –> click “Manage Extensions” –> find uBlock Origin –> click the “three dots” icon –> choose “Preferences”
   • click the uBlock Origin icon in the browser toolbar (if you have it pinned) –> click the “three cogwheels” icon
   • right-click the uBlock Origin icon in the browser toolbar (if you have it pinned) –> click “Manage Extension” –> click the “three dots” icon (top right) –> choose “Preferences”
2. Go to the “My filters” tab
3. Make sure “Enable my custom filters” is checked (enabled)

4. Add the following two lines: ###copilot-dab-main-button ###CopilotDABContainer

5. Click “Apply changes”

When you reload the site in question, the Copilot icon should either be completely gone (O365 web) or empty and non-interactive (Outlook).

uBlock Origin Lite (Chrome/Chromium)

Maybe Edge as well, since that's based on Chromium?

Since Chromium/Chrome-based browsers introduced MV3 as a way of allowing certain parties to buy-in to a list which stops adblockers from blocking their domains, uBlock Origin no longer works on them. uBlock Origin Lite is how I've managed to make this work on that browser.

You can get uBlock Origin Lite from the Chrome Web store

NOTES:

• The uBlock Origin Lite notes make it clear that it does not play well with other adblockers. If you have other adblockers installed, this may not work or may go weird.
• If your browser is part of a “fully managed” environment, your admin may have the power to block you doing this, in which case all I can say is “sorry for your lots”

With that out of the way, here's how it worked for me:

1. Open the uBlock Origin Lite preferences page using one of the following methods:
   • Click the “Extensions” browser toolbar icon (looks like a jigsaw puzzle piece) –> click “Manage extensions” –> find “uBlock Origin Lite” –> click “Details” –> click “Extension Options”
   • Right-click the “uBlock Origin Lite” icon in the browser toolbar (if you have it pinned) –> click “Options”
   • Click the “uBlock Origin Lite” icon in the browser toolbar (if you have it pinned) –> click the “three cogwheels” icon
2. You will have to set the default filtering mode to “Complete” for cosmetic filtering, which is what this is
3. Go to the “Custom filters” page
4. At or near the top of the page, you should see a grey section with just ... in it. If you hover over that section with the mouse, it should go black and the mouse pointer should change into the “text” cursor. Click in it so that you can type into it.
5. Type outlook.cloud.microsoft and hit Enter. You should be rewarded with a new, slightly indented, darker grey section with ... in it, underneath the site name you've just typed.
6. Click on the new, slightly indented, darker grey section with ... in it
7. Type button#copilot-dab-main-button and press Enter

At the moment, I haven't got it blocking the copilot button in Chrome on the O365 apps; for some reason, uBlock Origin Lite does not want to play the game.

If sufficiently motivated, I may try more and follow up here.