Some classes (for example, book and report) set up a
different set of footnotes per chapter, by resetting the footnote
number at the start of the chapter. This is essentially the same
action as that of
equation, figure and table numbers,
except that footnote numbers don’t get “decorated” with the chapter
number, as happens with those other numbers.
The solution is the same: use the chngcntr package; since the
numbers aren’t “decorated” you can use the \counterwithout*
variant; the code: