This has been a fairly recent change (~ within the past week) in Slashdot's Discussion 2 system. The "next unread comment" keybind (F) no longer works. Pressing F instead focuses on the search field.
I have tried Firefox 3.0.10 (both Mac/Win versions) and Safari 3.2.3 (Mac).
It seems like some javascript was changed so that there are multiple functions trying to run at the same time with certain keypresses. For example, 's' should "Previous/Next Comment Sibling W/S". However it does this AND jumps to the top of the page. 'd' should "Previous/Next Comment (Following Threads)", but once 's' has been pressed, 'd' both performs that function as well as jumping to the top of the page and collapsing the article summary.
It's like the firehose shortcuts got included in the main page (or on the comments.js) and now they're competing for keypresses.