User is able to get a full page error if they preview a reply on a paginated thread and then click any of the pagination links. I'm fairly certain this was filed on forums way back when. 1) https://master.support.mozilla.com/en-US/kb/brand-new-test-article/discuss/27 2) enter reply in box 3) click preview 4) click any of the pagination links for the discussion expected: go to that page and lose the reply, or a warning or something actual: 405 empty page view
This probably also affects the regular discussion forums. I'm marking it as P5 for 2.3 but it's priority will increase over time until it's done.
I am not able to reproduce it on article discussions.