[teo_zero]

Why reader mode?! It simply strips all styles and only retains contents. This webpage has no style, so reader mode should do nothing. If you see differences, it means your browser has different defaults for reader mode and normal mode. Choose which you like most and set it as default.

[mejutoco]

I suspect because reader mode has a reasonable max line lenght, and OP was complaining about that not being set on the page.