Some sites like Quora prompt for you to sign in before reading the first answer.  These posts appear in Google searches.  Rather than signing up for an account, you can use AdBlock plus to read the post.

Click the AdBlock Plus icon and choose Block Element.

The menu will disappear and when you hover your mouse over different areas on the page, it will highlight in yellow.  This is the element that will be blocked.  In this example, you can kind of read the post through the opaque layer, but it would better to just see it plainly.  Highlight the large transparent area and left-click.

A new window will appear showing what element will be blocked.

Click Add and the transparent layer will now be gone and you can clearly read the post.

Other Uses

This trick also works great on those annoying toaster slideouts or “Chat Now” windows.  It even works for those full-page popup ads with the little x’s.