Steps to replicate

1. Login into Confluence in Firefox browser.
2. Edit a page (CTRL/CMD+E).
3. In the editor, search (CTRL/CMD+F) for any string/word for example "and" and press Enter.
4. Confluence correctly finds the first matching occurrence and highlights it.
5. Clicks on "Next" to search for next matching occurrence.

Expected Behaviour
Confluence will highlights the next matching occurrence.

Actual Behaviour
Confluence stays as is and subsequent occurrences of the search term are not found.

Workaround
Use different browser (Chrome/Internet Explorer) or the browser's "Find in This Page..." menu option.

Notes
This feature was working before the update of Firefox version 63.0