Adding 52 comments in a batch review breaks the browser

I added 52 new comments in a review.

Before submitting the review I switched from the diffs tab into the discussion tab, the discussions tab had a lot of whitespace after the main comment textarea which made it super hard to find and to submit the review.

After I submitted the review, the browser froze, the scroll stopped working. Then this happened:

Screen_Shot_2018-10-18_at_14.32.49

After a few minutes (3/4min) the browser went back to normal and I could finish my comment

/cc @andr3