for firefox: https://addons.mozilla.org/en-US/firefox/addon/re-enable-right-click/
install the extension, visit the OF page and click the extension icon once. Now when you right click inside the video you'll se the "Save video as"
it's the method I use, i've suggested it here before and some people said the save video option is greyed out for them, so... you'll need to check if that's your case.
