HTML5 editor misaligned text

[Rebecca Lopes]

I'm trying to edit a theme on tumblr, but the cursor don't align with the code text (image).

Is not a tumblr problem because it happened on generalassemb.ly code editor too. And it's not an extension problem either, because I've tested on an incognito window, and dissabled all the extension and restarted the browser and the problem still the same. I'm using both editors on firefox and they work fine.

Does anyone know how to fix this?