Soft Ad Block
About
Soft Ad Block is a browser extension that blurs advertisements. All ads remain in their places, so we can see how many ads there are, but the content of the ad is blurred. This can be useful if you want to share a screenshot or screencast of a website but don't want to share ads as well. So instead of blurring ads in final image (or video) you can use this extension and get all the ads blurred while capturing.

The extension is written in CSS so not all the ads can be blurred, plus I haven't update the blocking rules (selectors) for a long time, so it is more like a concept of what CSS can do.
Try it out
Sources
The sources can be found on Github: