firmness vs foible

firmness

noun
  • security; steadfastness; good grip 

  • strictness; mental strength 

  • physical durability; rigidness (of material) 

foible

noun
  • A quirk, idiosyncrasy, or mannerism; an unusual habit that is slightly strange or silly. 

  • A weakness or failing of character. 

  • Part of a sword between the middle and the point, weaker than the forte. 

How often have the words firmness and foible occurred in a corpus of books? (source: Google Ngram Viewer )