I appears that Firewalker’s Boots are bugged and never grant haste.
I have run a test of over 100 turns with 5 - 15 red gems on the board in any given turn, but have never seen the haste effect. Either the item is broken or the RNG is broken. Based on @AeonNhiyr’s and my season 1.3 cache numbers I suppose both are possible. 
Steps to reproduce:
Equip Firewalker’s Boots
Play game
Never get haste
Same experience. I have the boots at legendary and even with 9-12 red gems on the starting board which puts a potential 31.5%-42% for haste, I still get nothing. It seems the boots are just stuck at giving the initial percentage (the 3.5% for legendary) and not counting the red gems. Please investigate the passive.
Just gave this a test on my Necromancer in a Dungeon battle, and upon the start of my first turn against the second opponent I triggered Haste.
I don’t have any other gear that can trigger Haste either.
But following up with the team to confirm this is calculated correctly and as intended.
Update: It appears it was calculating lower than intended, still calculating upon each red Gem at the start of your turn, but the team will get that resolved.
Not sure if that will go out with 2.1 or earlier at this stage.
Note: This is my normal/personal account
