Hook up the browser to a proxy intercepter such as Burpsuite.
If you dont want to install it, you can use the "HTTP Recorder" option from the top left bar.
Find every domain or locate the script file for ads placements.
Then use "Request mask deny" from Network tab (NOT Cache Mask Deny thats another thing)
For every ads network domain, add it on Request Mask Deny option like this
*doubleclick.net
*taboola.com
*googlesyndication.com
Note that * is wildcard option.
This will block all requests to any subdomain of the URLs.
Or if the ad function is from external js file add "*adfile.js" as deny