Aside from reporting it as suggested.

I have just gone to the hXXp://www.adobe.com/products/flash.html page that you mention, without an avast alert (using firefox 30.0), though your image shows much more in the URL. The /…/ concatenation obscures the full URL.

So can you confirm exactly the page you were on (break the URL as I have above using hXXp to avoid accidental exposure.

Or was it when you used one or other of the buttons on that page ?

Normally with that URL:Mal it is a link to a third party site that is considered malicious, not necessarily the page you were on. But for anyone to try and investigate this they would need the exact actions you were making and the URL you were on when you got the alert.