\documentclass[12pt]{book}
\usepackage[a4paper,noheadfoot,nomarginpar,margin=20mm,showframe]
 {geometry}


% adjust this value to suit
\def\foottableraise{2ex}

% define a new environment
\newenvironment{foottable}{%
 \raise\foottableraise\hbox\bgroup\space
 \begin{tabular}[t]%
 }{%
 \end{tabular}\egroup\vskip\foottableraise
 }

\begin{document}%
 xyz\footnote{%
   \raisebox{\foottableraise}{ % inserts a space
   \begin{tabular}[t]{|l|}
      \hline
       abc\\
       def\\
       ghj\\
       klm\\
       abc\\
       def\\
       ghj\\
       klm\\
       \hline
     \end{tabular}%\\
     }%
     \vskip \foottableraise
   }
 xyz\footnote{%
   \raisebox{\foottableraise}{ % inserts a space
   \begin{tabular}[t]{|l|}
      \hline
       abc\\
       def\\
       ghj\\
       klm\\
       abc\\
       def\\
       ghj\\
       klm\\
       \hline
     \end{tabular}%\\
     }%
     \vskip \foottableraise
   }
\newpage
 xyz\footnote{%
   \raisebox{\foottableraise}{ % inserts a space
   \begin{tabular}[t]{|l|}
      \hline
       abc\\
       def\\
       ghj\\
       klm\\
       \hline
     \end{tabular}%\\
     }%
     \vskip \foottableraise
   }
 xyz\footnote{%
   \raisebox{\foottableraise}{ % inserts a space
   \begin{tabular}[t]{|l|}
      \hline
       abc\\
       def\\
       ghj\\
       klm\\
       \hline
     \end{tabular}%\\
     }%
     \vskip \foottableraise
   }
\newpage
 xyz\footnote{%
   \begin{foottable}{|l|}
      \hline
       abc\\
       def\\
       ghj\\
       \hline
     \end{foottable}%\\
  }
 xyz\footnote{%
   \begin{foottable}{|l|}
      \hline
       abc\\
       def\\
       ghj\\
       \hline
     \end{foottable}%\\
  }
\newpage
 xyz\footnote{%
   \begin{foottable}{|l|}
      \hline
       abc\\
       def\\
       \hline
     \end{foottable}%\\
  }
 xyz\footnote{%
   \begin{foottable}{|l|}
      \hline
       abc\\
       def\\
       \hline
     \end{foottable}%\\
  }
\newpage
 xyz\footnote{%
   \begin{foottable}{|l|}
      \hline
       abc\\
       \hline
     \end{foottable}%\\
  }
 xyz\footnote{%
   \begin{foottable}{|l|}
      \hline
       abc\\
       \hline
     \end{foottable}%\\
  }
 xyz\footnote{%
   \begin{foottable}{|l|}
      \hline
       abc\\
       \hline
     \end{foottable}%\\
  }
\end{document}%