nsIWebBrowserPrint.globalPrintSettings returns a new object each time. That is
why the code in these tests doesn't work, and why they have the workaround to
set the pref to disable the progress dialog. This patch fixes the code and
removes the prefs setting workaround.
This patch also changes the code to use the print settings service to get the
print settings. That's all that nsIWebBrowserPrint.globalPrintSettings does
anyway. Making this change allows me to remove
nsIWebBrowserPrint.globalPrintSettings in the next patch.
Differential Revision: https://phabricator.services.mozilla.com/D83279
dc75460193