I mean the code on the backend.
try to put the below before tap(done)

import pdb; pdb.set_trace()

and do this in pdb:

import re; import codecs; f = codecs.open("temp","w","utf8"); f.write(re.sub(r'<(script).*?</\1>(?s)', r'', self.marionette.page_source))

and then

n

to go through the tap(done) step, and then do

import re; import codecs; f = codecs.open("temp2","w","utf8"); f.write(re.sub(r'<(script).*?</\1>(?s)', r'', self.marionette.page_source))

After these, try to compare the source code from temp and temp2, you should find that even if the screen switch back to Usage app main screen. The backend source code remains unchanged.