jsfiddle js panel size is stuck! How do I reset it?

Please run Layout.setWindowSizes(null) from console

https://github.com/jsfiddle/jsfiddle-issues/issues/493

As of December 6, 2018, the current answer to this question no longer works due to a rewrite of the JsFiddle site that happened sometime in June/July of 2018.

1. Press F12 to open DevTools (Chrome) or Debugger (Firefox, Edge).
2. Navigate to "Application" in Chrome DevTools, or "Storage in Firefox/Edge Debugger.
3. Find "Local Storage".
4. Find www.jsfiddle.net.
5. Delete any entries/keys labeled as grid_*-split-sizes (eg. grid_1-split-sizes, grid_2-split-sizes, grid_3-split-sizes).
6. Refresh jsfiddle.net webpage.

Source: https://github.com/jsfiddle/jsfiddle-issues/issues/1151