If you are trying to edit a custom field context, it is very easy to accidentally delete it. It is poor UX and there has been an open ticket asking Atlassian to fix it for 6 years today: JRASERVER-27957 We wanted to commemorate this occasion by sharing a simple workaround. Just put this in your announcement banner and voilà, warnings before deletion.
If you’re on Cloud, you can’t inject this kind of content into the system. But you can have your admin team inject it via their browsers. The popular tool for this is Tampermonkey which is available for almost any browser.