Believe this is intentional behavior on Firefox's end. It tries to preserve the data you've entered into forms when you refresh the page. Toggle switches are HTML checkboxes under the hood.
With JS enabled, clicking a toggle switch saves the new state immediately, so you don't encounter this behavior with toggles when JS is enabled, but you do run into it elsewhere:
- Use Firefox - JS enabled or disabled, it doesn't matter
- Go to https://kagi.com/settings?p=custom_css
- Change something in one of the text boxes; don't save
- Refresh the page
- Text box keeps its value
- Click Appearance link, click Custom CSS > Change link to navigate back to /settings?p=custom_css, notice it shows the old value again