I’m having the same problem. Works in Chrome (which I don’t really use) and not in Firefox. Keep on getting the note that I have to be logged into Harvest even though I AM logged into Harvest, in the same browser.
I had to download Asana for Windows to be able to track time, but unfortunately, it doesn’t display the total time spent on a task. I contacted Asana support and I’m not sure if they will work on a fix since they said to use Chrome.