1364980 - Javascript is inefficient

Status: RESOLVED INCOMPLETE

(Firefox :: Untriaged, defect)

Description

[Jim Moe]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0
Build ID: 20170413000000

Steps to reproduce:

Sites that use Javascript can be very slow and greedy with CPU usage. Though the resource monitor indicates that only one CPU (of four) is at 100% usage, FF is mostly or totally unresponsive until whatever JS is looping is complete.

Some examples:

The current Lastpass plugin.

This is a good example although you need a subscription. It is the DVD queue listing.
<https://dvd.netflix.com/Queue?qtype=DD&lnkctr=mhbque>

Facebook login screen:
https://www.facebook.com/login.php?next=https%3A%2F%2Fwww.facebook.com%2Fn%2F%3Ftaotuc%252Fposts%252F10154251253947723%26medium%3Demail%26mid%3D54f81a0448accG5af383f14ea0G54f81e9da8d9eG318%26bcode%3D1.1494794275.AbluErcLrumPBwpL%26n_m%3Dmoe.james%2540sohnen-moe.com&email=moe.james%40sohnen-moe.com

New York Times front page:
<https://www.nytimes.com/>


Actual results:

While the site (or plugin) is loading, or thinking, FF is barely responsive, sometimes not at all. This does not occur on sites that use no or very little JS. The CPU monitor shows that one CPU (of four) is at 100% usage.


Expected results:

Some of the time is downloading libraries and markup. However, the network monitor shows only a brief activity while FF continues to apparently do nothing for a few to tens of seconds.

But since other browsers (Chrome, Opera) can load these site much more quickly, without the unresponsiveness, I suspect an inefficiency in Javascript.

Comment 1

[Kohei Yoshino [:kohei]]

Please test with Safe Mode: https://support.mozilla.org/kb/troubleshoot-firefox-issues-using-safe-mode
Also follow these instructions: https://support.mozilla.org/kb/firefox-slow-how-make-it-faster