It looks like this might be a symptom of a bug in Aquamacs that has supposedly been fixed. See this discussion
It seems like the user in that post was able to solve the problem by running:
from the terminal to create the missing file. You can try this, our try creating the file from emacs by calling
C-x C-f (
find-file), entering the complete the path
/Applications/Aquamacs.app/Contents/Resources/etc/publicsuffix.txt and confirming that you want to create the file which seems to be missing.
The issue is that the function
url-domsuf-parse-file is expecting to find that file, and it isn't where it should be. I am not sure what the consequences are of putting an empty file in its place, but it is worth a try. I guess you could even paste in the contents of this file, because I assume that is what it is looking for.
Finally, if you are using an outdated version of Aquamacs, you should update if possible, and the problem will likely fix itself.