Alright. I took a look at this. First off, looks like you took the script from the Barbarian Rage which runs post-levels/10000. That's too early to determine your CON bonus. However, if you move the whole script to post-attributes then nothing else works. So, I recommend you move that last piece to a new script.
Second, you want to use the field "aBonus" instead of "Bonus". The former is your CON bonus before modifiers, while the latter is used for untyped bonuses to your CON score.
Post-Attributes/15000
Code:
~ We can Fury based on our constitution + level rounds per day
~ times per day.
var total as number
total = 2 + (field[xTotalLev].value * 2) + hero.child[aCON].field[aBonus].value
field[hTotal].value += total
field[livename].text = "Fury (" & total & " rounds/day)"
PS. If you right-click on your CON score and select "Show Debug Fields" you can see how the fields change when you are enraged. This tells you which field you want to use for this purpose.