Search in all JS/CSS files in Firefox
Solution 1:
- Press F12 to open the Developer Tools.
- Click the Debugger tab (if it isn't visible, click ❱❱ and select it from the list).
- Press Shift+Control+F.
https://developer.mozilla.org/en-US/docs/Tools/Debugger/How_to/Search#searching_in_all_files
Click on any entry in the list to go directly to the line in the file where the string occurs.