On both my Nexus 5X and Nexus 9 running Firefox, selecting a message in the new mobile chat interface is extremely slow, pegging one CPU core for several seconds before the options appear in the top bar. It appears the animation used when showing the buttons in the top bar is difficult for Firefox to process. However, the animation plays smoothly under Chrome.

Is this something you can optimize for, or is Firefox to blame?

  • I can repro. Actually, I originally wrote it off as having about 400 tabs open, but it's good to know it's not that.
    – Bob
    Mar 9, 2016 at 2:12
  • Everything is very CPU-intensive under Firefox for Android :\ FWIW that animation is a CSS transition. (Don't get me wrong, I like FF and actually use it quite a bit on my phone -- but it doesn't exactly fly).
    – balpha StaffMod
    Mar 9, 2016 at 5:29
  • Dug a little deeper and it seems this is a known problem: bugzilla.mozilla.org/show_bug.cgi?id=754475
    – bwDraco
    Mar 9, 2016 at 7:00

1 Answer 1


Ok, I'm going to do a bit more digging here. I'll just use this answer to record what I can find.

Unfortunately, I suspect SE won't be too happy about sharing the unminified chat source so producing a minimal repro is going to be a bit difficult. We'll see.

  • It's actually one shorter FPS dip while it renders, followed by another much longer (7s) one after the menu is displayed but before any further presses are registered.

    enter image description here

  • Definitely something funny going on with graphics. 7 second paint?!

The next step would be to use the advanced Gecko profiler. Unfortunately, I'm told that that profiler has not worked with Firefox for Android in a while.

Another thing would be trial and error but that's probably easier for SE to test.

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