If I copy code from my local text editor (I tried it from three different ones) and paste into Repl.it, my browser almost crashes ("a website is slowing down yr browser" message from Firefox) and when it's done pasting, the formatting looks like a staircase going down from left to right. This occured the first time for me today.
Update I also tried it from opera browser, where this problem does not occur - only Firefox!
Do you have a link to your code? is it the same code?