STR: 1. Open Gmail in logged in state 2. Mouse click the first email in the inbox 3. Click on the “reply” button on the top right corner of the email Reports: https://goo.gl/V7un6P Notes: https://docs.google.com/spreadsheets/d/1MsTK1FW88wuLd25A18HG2KqpjYJnvrxGM9a6MeZp35w/edit#gid=256706414 Firefox Profile and Chrome Tracing will be attached in the following.

Firefox Profile: https://perfht.ml/2qRUPH3 Chrome Tracing: https://goo.gl/79Zl9W

Short Gecko Profile(cover only Input Lantency action): https://perfht.ml/2riI6gV

(In reply to myen from comment #2) > Short Gecko Profile(cover only Input Lantency action): > https://perfht.ml/2riI6gV In the range that we received the mouse click event: https://perf-html.io/public/98aac49936ca0f5bb109fd0d0e2e48f86152d786/calltree/?range=2.0205_3.2994&thread=5 We spent 504 ms in running the event handler: https://perf-html.io/public/98aac49936ca0f5bb109fd0d0e2e48f86152d786/calltree/?callTreeFilters=prefix-07xOu&range=2.0205_3.2994&thread=5 Which was followed by refresh driver ticks: https://perf-html.io/public/98aac49936ca0f5bb109fd0d0e2e48f86152d786/calltree/?callTreeFilters=prefix-0123456789abcde9abBiDBhvx0&range=2.0205_3.2994&thread=5 The question is: why we need to spend 504 ms running the click handler of the reply button? One thing that catches my attention is js::jit::DoCallFallback() is called in may places in this range: https://perf-html.io/public/98aac49936ca0f5bb109fd0d0e2e48f86152d786/calltree/?implementation=cpp&range=2.0205_3.2994&search=DoCallFallback&thread=5 I am not sure if this explains why we need to spend so much time in JS. We need a JS expert to take further look.

Sean, could you help to follow Cervantes's investigation? Thanks.

Too much cases on Sean. Ping Marcus instead. Thanks.

Marcus, can you please do a profile analysis on this?

I don't think I have anything to add to Cervantes' analysis. The click handler is running JavaScript, and it's really hard to say why that JavaScript is taking longer to run than it does in Chrome, at least for me.