2018.09.19 00:22:56 (1042177178497155072) from Daniel J. Bernstein, replying to "thomas greenhalgh (@likothecat)" (1042174263027879936):
In Firefox, the relevant button is "Switch to Presentation Mode" (four arrows pointing outwards). In Chromium, it's "Fit to Page" (also a four-way icon). In both cases, left and right arrows move between the successive displays as expected.
2018.09.19 00:11:21 (1042174263027879936) from "thomas greenhalgh (@likothecat)":
nor in chrome on a mac - pretty sure the file itself is messed up