Unfortunately this is only available in windows. However, you can install an extension from the chrome store that adds this functionality. First you have to install the "Download Chrome Extension" from the Opera addons store, and then you can install the chrome extension.
https://addons.opera.com/extensions/details/download-chrome-extension-9
https://chrome.google.com/webstore/detail/autoscroll/occjjkgifpmdgodlplnacmkejpdionan