Although the "replace" function is not useful on pages the user can't edit, such as
https://en.wikipedia.org/wiki/MediaWiki:Common.js?action=edit
the "find" function is still desirable (mainly because browsers usually doesn't allow regex search when using CTRL+F.
Version: unspecified
Severity: enhancement
Still valid in git master; though might require some JS knowledge to find the right place where the check for page protection is actually done.
The WikiEditor isn't even loaded on protected pages (at least not since https://en.wikipedia.org/w/index.php?title=MediaWiki:Common.js/edit.js&diff=603166167&oldid=565609564 was fixed).
The CodeEditor will be available in read only mode after Bug 45258 is fixed. Therefore, I'm closing this as wontfix for now.