In the frames view of a webrev, the BOF, EOF, Scroll {Down, Up}, and {Next, Prev} Diff navigation buttons no longer work. This appears likely to be due to this fix

https://www.mozilla.org/en-US/security/advisories/mfsa2019-21/#CVE-2019-11730

as linked from the Firefox 68.0 release notes

https://www.mozilla.org/en-US/firefox/68.0/releasenotes/

If the webrev is copied to cr.openjdk.java.net the navigation buttons still work.

Note: Frame navigation in a local webrev does not work for Chrome, Opera, or Safari either.