For unknown reasons I cannot change the once-set homepage URL in Safari (v10.1 on OS X 10.11.6) any more. If I change it in Safari's Preferences window, under General, it simply resets it to the value it was set to before. Same when I use the "Set to current page" button.
The same problem is with Safari 10.1 on another Mac running 10.10.5. I wonder if it's because they're both using iCloud, sharing their bookmarks. However, the homepage is set to a different page on each Mac, which suggests that this address is not synched with the bookmarks (which is good, IMO). And turning off iCloud Safari sharing doesn't help, either.
So I am trying to figure out where it stores the URL on disk, so that I can check if that is somehow locked.
However, I cannot find the current homepage URL in various places. Neither in the Safari preferences file (~/Library/Preferences/com.apple.Safari.plist) nor in any file inside ~/Library/Safari/ (including Bookmarks.plist) and ~/Library/WebKit/, at least not in plain ASCII text.
Where is that URL stored?