with a little bit of scripting/keyboardmaestro, can compare webpage text to yesterday's captured version e.g. set keyboardmaestro to capture the current text, then run

#!/bin/bash
DATE_TODAY=$(date +"%Y%m%d")
DATE_MINUS=$(date -v -1d +"%Y%m%d")
FILE_CONTENT=$(pbpaste)
echo "$FILE_CONTENT" >> /path/"$DATE_TODAY"filename.txt /usr/local/bin/ksdiff /path/"$DATE_MINUS"filename.txt /path/"$DATE_TODAY"filename.txt