Just yesterday I learned that on an ISO Spanish keyboard, both of those browsers will pop up a help menu for ⌘⇧7. The logic goes: ⇧7 means / on a Spanish ISO keyboard, and ⇧/ means ? on a US-ANSI keyboard, therefore ⌘⇧7 is by the transitive property of inter-layout shift functions equivalent to ⌘?, which is the shortcut for opening the help menu.
They don't pop open the help menu if you press ⌘⇧', the actual ISO Spanish layout way to type ⌘?
Something like http://www.keyboard-layout-editor.com/#/gists/9150730dbd4d28...
Page down only sometimes works, and Command+~ to switch same app Windows works in some apps and not others. It's a bit of a train wreck when you want to get rid of their pointless keys.
Although macOS is good in the aspect that combinations akin to AltGr on PCs aren't unique to non-US layouts. I've seen programmers assume it's safe to assign shortcuts to Ctrl-Alt (which simulates AltGr), making it impossible to enter certain characters. Not surprising, as it's not used on the US layout (just as there's no extra key next to the left Shift).
Amusingly, TextMate's author and many early users were European programmers with US-ANSI keyboards (because the various European layouts are just too painful for writing code in ASCII-based programming languages).