Command Backtick isn't working to cycle through windows in some apps (including Safari)
Solution 1:
This has bugged me since i got my MacBook but have just managed to fix it by doing this:
"going to System Prefs, Keyboard & Mouse, Keyboard Shortcuts, Keyboard Navigation, and click on Move focus to next wondow in active application. There may be other shortcuts that you can restore there, too." taken from From http://discussions.apple.com/thread.jspa?threadID=1776080:
Then change the shortcut to apple key + `
Hope this helps as I know it's such a pain not being able to quickly switch between windows, particularly in Safari.
Solution 2:
For those who have an international keyboard, the command might be assigned to a key combination that is not produced by the Cmd + ' (i.e. the button to the left from key "1"). This even if the original key combination looks correct on the screen. To fix this go to System Preferences -> Keyboard and reassign the "Move focus to next window" to Cmd + '. This on Mojave. Took a while to figure out what was wrong...