Use symbols for the footnotes, and reset the counter on each frame.
Using numeric indicators can be confusing when they appear next to a
number (such as a year) because they look like exponents. We also do
not need to preserve the counter across slides; the audience can see
only one slide at a time. Finally, we skip the asterisk (the first
default symbol) because it is ugly / wide.
{ \end{frame} }
+% Reset the footnote counter on each slide, and always start
+% from the dagger (i.e. skip symbol zero, the asterisk).
+\renewcommand{\thefootnote}{\fnsymbol{footnote}}
+\AtBeginEnvironment{frame}{\setcounter{footnote}{1}}
+
\mode<all>