Undo
After every change, an Undo button appears in the top bar for 24 hours. Hover over it to see what it will undo. It restores the settings from before your last change and clears the cache.
Settings history
Every time settings change, a snapshot is saved. Open the Tools tab to see Settings history. Click Restore on any entry to go back to it. Up to 50 snapshots are kept.
Restoring is also saved in the history, so you can always go forward again.