To me, having a recommended browser for a site goes against everything Sir Tim's marvelous invention stands for. So, we are not targeting or recommending any browser at the moment. Having said that, it would not be possible to support any browser, however old. I use EDA Playground regularly on Chrome, Firefox and Safari and it seems to work equally well on all three, but I know that EDA Playground doesn't work properly on my mobile phone (Chrome on Android), for example, and I would like to fix that. But there are many other things in the To Do list...
Matthew