If I leave MN and look at a different tab for a while, or go away and do something else when leaving it open, it is non-responsive on my return. None of the browser buttons work, none of the links work etc. I have to totally close it and reload it again from bookmarks. It's been doing it on occasion (or loading very slowly) since the supposed upgrade, but much more so in the last couple of days. Makes it unusable over longer periods of time. Something is slowing it down so much that it finally stops.
Firefox on a desktop mac.