This not a support question. There are other places for this subject. No further responses will be made to this post as you are not having a technical difficulty with Firefox.

For further info please read this https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

There are also extensions that can slow it down but look for Fat-Free Fox and see if that helps you.

I tested with fresh Firefox with no add-on installed. also I know enough about solving performance issues, I posted this just to alarm Mozilla's guys.

BTW JetStream supposed to test browsers itself not browser that armed with some add-ons.

Thanks @Pkshadow for your time.