What version of Opera are you using ?.
If it's the newer Blink version of Opera (15.x-23.x) then you could try looking on the Chrome webstore https://chrome.google.com/webstore/category/extensions for an equivalent extension.
You will need to install the 'Download Chrome Extension' https://addons.opera.com/en-gb/extensions/details/download-chrome-extension-9/?display=en first, which allows you to install compatible Chrome extension in Opera.