Identify perf needs for upcoming release

[mcomella]

It's soon so we need to do this soon.

• [x] Find out nightly branch date, last train (already too late?)
  • I think it's already in Beta so it'd be the next release that splits on 5/31
• [x] Figure out what changed, if anything. Is there a special branch to test on?
• [ ] Run startup and pageload tests as well as profiling as sanity check
• [x] Follow-up on item 2: anything else to test?

[mcomella]

I found a rough list of what changed: https://support.mozilla.org/en-US/kb/whats-new-firefox-android-79?redirect=no

I think we should look into:

• [x] How long does the menu take to open in the new version vs. the old version?

[mcomella]

How long does the menu take to open in the new version vs. the old version?

I took screenrecordings w/ timestamp information embedded and compared them (granted: we don't know how reliable this method is or how noisy the interaction is). Between FF 88.1.4 (old) and nightly 91.0a1 6/3 @ 5:05 PM, we see…

• From the initial tap until the menu animation starts, a 73ms improvement (401ms old, 328ms new)
• From the initial tap until the menu animation completes, a 81ms improvement (493ms new, 574 old)

Anecdotally, the new version seems slightly slower but it's so close I shouldn't be able to detect a difference.

Seems good enough to me!

[mcomella]

We've been running the start up tests on FNPRMS so I think we're good here.