iMacros is causing big problems in firefox 73.0 and 73.0.1 that did NOT exist with firefox 72.0.2. Specifically, switching to a different tab in a session tales about 20x as much time as before, say 20sec instead of 1sec. Disabling iMacros makes the problem go away. See also https://old.reddit.com/r/firefox/comments/f5oa4u/firefox_7301/fi2tizq/