During debugging 848316 I noticed that it is really hard to find bugs that are caused by a busy main thread. We should add annotations when events are delayed for maybe > 100 msec or if there is no advance in the event loop. I am scared that we have more bugs like this in gaia. I don't know how hard this is to implement but it would be super useful!
FYI there are a few lag-measurements like https://bugzilla.mozilla.org/show_bug.cgi?id=710935, https://bugzilla.mozilla.org/show_bug.cgi?id=706916
We have event loop lag indicators in cleopatra these days. I think that's what was asked for in this bug.