I`ve just experimented with this once.
I gathered the leaves and some flowers in a bag, about 2-3 litres worth.
Let it sit for a day (room temp) to "ferment".
You will see that the leaves get a little bit "floppy" when they are done.
Then I rolled a good pinch of leaves between my palms.
Do that until all the leaves are broken down. Then lay it out on a baking tray and dry it in the oven (low heat, door open) overnight.
The brewed tea is of right color, but tastes a little like green tea blended with dry grass.
Guess it is best blended with black tea.
I have read that tea in Russia in mid 19th century could contain as much as 60 percent fireweed.