Looping scroll with PageDown in MR discussion

Summary

Looping scroll within the merge request discussion tab. This may not be limited to this tab. Using arrows seems to reset it to the normal behavior.

I'm on Firefox 57b7 on Linux.

Steps to reproduce

I'm not really sure. This happened once before, but a refresh destroyed the state. This time I was reviewing an MR in the diff tab, made some comments, and then went back.

What is the current bug behavior?

Holding PageUp will go to the top, but PageDown will loop around to one page below the top.

What is the expected correct behavior?

PageDown should stop at the bottom.