I had a similar problem in my project. Luckily, whenever I needed to set focus on already opened tab, it also needed to be refreshed. So I did it with the following trick, which first opened again tab with same href and target, got reference of that window back, closed it, and opened again with same parameters.
popup = window.open('/popup.html', '_popup')
popup.close()
popup = window.open('/popup.html', '_popup')