The deployed solution to T300069 (showing the correct message title when viewing with qqx) has bad side-effects when the string '$/' exists in a banner. Fundraising banners that include regexes are throwing JS errors 'Unterminated regular expression literal'
Could we revert https://gerrit.wikimedia.org/r/c/mediawiki/core/+/761486 or update it with a different delimiter that doesn't break regexes?
Note: It happens that Fundraising banners are not live right now. However, this also breaks FR banner previews, needed to test banners that are expected to go live shortly.