'Classic' CSS tweaks for Firefox 57+ v1.6.6.1

Changes since 1.6.6: 72c9b72
Changes since 1.6.5.1: bfdf817

[General UI]

• (new) old search (known from Classic Theme Restorer)
  • 'about:config > browser.search.openintab': open search in current or new tab
  • 'about:config > browser.search.suggest.enabled': search suggestions visibility
  • it is possible to edit searches xml file to enable "clear input after search"
  • it is possible to edit searches xml file to enable "revert to default engine after search"
  • search engines popup and search popup will use search boxes width