OptOut10 (Mozilla Firefox)
 
 

    Look familiar?  Here's how to get rid of that nasty Windows 10 advertisement on MSN in Mozilla Firefox:
  1. Install the Firefox UAControl extension.
  2. You shouldn't need the added UAControl Firefox toolbar button, so feel free to right-click it and click Remove from Toolbar.
  3. Triple-click the line of text below to select it, and press [Ctrl]+[C] to copy it to your clipboard.
  4. Mozilla/5.0 (Windows NT 10; WOW64; rv:43.0) Gecko/20100101 Firefox/43.0

  5. Visit www.msn.com (or whatever site is giving you the blocking Windows 10 advertisement).
  6. Right-click a blank area on the page and click UAControl options for this site.
  7. Tick the Custom option.
  8. Press [Tab] and then [Ctrl]+[V] to paste the copied text into the Custom textbox.
  9. Click [OK] twice, and then refresh the MSN page.  The Windows 10 ad should be gone.
  10. Repeat steps 3–8 for any other site that is exhibiting this behavior.

I hope this helps someone!  Comments or suggestions?  Feel free to leave them here.