Ok, this isn't new, but it is new to me. You can add this "favorite" to your browser and when you click on it, it turns all DWF links into thumbnails. And if you click the thumbnail, it brings up the DWF in a viewer. Free & Easy!
Here are before & after shots. First I searched "filetype:dwf P&ID" then I picked the DWF-this-link bookmark:
Excellent instructions on how to do this found here:
Good name "bookmarklet" - it's a bookmark AND a little application (app-let).