By default LaTeX starts the footnote counter at zero for each chapter when you use the class {book} or {scrbook}. If you want to avoid that and have a continuous enumeration, here is how it works:

Create a folder <remreset> in your local package repository. Save the file remreset.sty into this folder.

Open your preamble and add

\usepackage{remreset}
\@removefromreset{footnote}{chapter}

Should you get an error message like this

You can’t use ‘\spacefactor’ in vertical mode. \@

or like this

Command \@ already defined.

embrace the stuff with \makeatletter and \makeatother:

\usepackage{remreset}
\makeatletter
\@removefromreset{footnote}{chapter}
\makeatother

Voilà.