Running custom javascript code and getting results back from page

Not sure if I can accomplish what I want to do with with what is available through wpt at the moment. This is a question more than a feature suggestion.

I need to execute some javascript code after a page is loaded then pass a json object to be analyzed with test results. So far I have been using the console to serialize this JS object and reading it back. It seems that getting the console output is only available for Chrome.

First question: Is it possible to get console output for tests run using IE or Firfox?

Second question: Is it possible to accomplish the above with some other feature in WPT I am not aware of that would work for IE and firefox?


Console output should be at the bottom of the screenshots page (but I haven’t checked this for a while)

Thanks for your reply.
It seems that the console output only works with Chrome when capture time line is checked or through the api by adding timeline=1.
This is a test using Chrome, with console output:
This is a test using Firefox, no console output:

Yeah, console log only works for Chrome right now. Been planning on adding it for Firefox but it hasn’t bubbled up my priority list yet (and IE but I expect IE will be significantly harder).