It's a simple number thing. The limit is 10^3,000,000 (novemnonagintinongentimillin-novemnonagintinongentillion). Press space to change the -illion number and press "s" to change the speed. If you acutally reached novemnonagintinongentimillin-novemnonagintinongentillion without using the spacebar, I think you should touch grass. Yeah, there's a ton of code inside. Seriously. Yes, I know I can make this work with -illions up to novemnonagintinongentimirc-novemnonagintinongentimillin-novemnonagintinongentillion, but that would just be way too many code and there's already tons of code used to make millinillions work.
Credit to @-Rex- for the text engine used here (Pen Text Engine++).