Oana Botisan, Desktop QA Reporter
	Description • 5 years ago

[Affected versions]:
- Firefox 64
- Firefox 65.0b4
- Nightly 66.0a1

[Affected platforms]:
- macOS 10.13
- Ubuntu 18.04 x64
- Windows 10 x64


[Steps to reproduce]:
1. In the URL bar, navigate to
       data:text/html,<script>while(true);</script>
2. Wait until the notification "A web page is slowing down..." is displayed.
3. Open at least three tabs.
 
[Expected result]:
- A New Window is opened and loaded.
- The notification "A web page is slowing down..." is displayed.

[Actual result]:
- A New Window is opened, but it doesn't load (the Activity Stream page is not loading).
- The notification "A web page is slowing down..." is not displayed.

[Regression range]:
- Last good revision: aff336ac161daa3ea350e59a288963edbd58ed39 (2017-07-17)
- First bad revision: dece50457378ac4934afe9fb3c2a8054e8894588 (2017-07-18)
- Pushlog:
https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=aff336ac161daa3ea350e59a288963edbd58ed39&tochange=dece50457378ac4934afe9fb3c2a8054e8894588

[Additional Notes]:
- Please look at the attached gif. 
- Sometimes the New Tab is loaded, but if you open another two tabs, the second one doesn't load. 
- I am not sure if I chose the Component correctly, feel free to change it.

	Dan Mosedale (:dmosedale, :dmose)
	Comment 1 • 5 years ago

(In reply to Oana Botisan from comment #0)
> [Steps to reproduce]:
> 1. In the URL bar, navigate to
>        data:text/html,<script>while(true);</script>
>
> [...]
>
> [Actual result]:
> - A New Window is opened, but it doesn't load (the Activity Stream page is
> not loading).
> - The notification "A web page is slowing down..." is not displayed.

If I wait a second or two, the "A web page is slowing down..." appears on all of the tabs, even it wasn't initially there on some of the subsequently opened ones.
 
> [Regression range]:
> - Last good revision: aff336ac161daa3ea350e59a288963edbd58ed39 (2017-07-17)
> - First bad revision: dece50457378ac4934afe9fb3c2a8054e8894588 (2017-07-18)
> - Pushlog:
> https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=aff336ac161daa3ea350e59a288963edbd58ed39&tochange=dece50457378ac4934afe9fb3c2a8054e8894588

This is the merge when activity-stream was turned on by default in mozilla-central.  So something did change about the nature of the home page content then, but, then, AS is a significantly more featureful thing than before, so it may just be that it's executing (more?) JS in content.

> [Additional Notes]:
> - Please look at the attached gif. 
> - Sometimes the New Tab is loaded, but if you open another two tabs, the
> second one doesn't load. 

The reason for this is because, given a short amount of idle time, a new tab is preloaded behind the scenes, so it dodges the bullet.  After that, if you immediately open another new tab, it won't have had time to preload something, so things are stuck.

Interestingly, if one sets the newtab preference to load a blank page, then enters the above data: URL, opens a new tab, and tries to load almost any kind of page (eg about:preferences, cnn.com, etc), those pages won't load either, until one of the "Stop It" button on the info bar is pressed.

So my guess is that there's nothing Activity-Stream specific here, but, rather, that most browser loads become dysfunctional if runaway JavaScript completely eats the CPU and the user doesn't press the stop button.  Ideally, this wouldn't happen for in-browser UI, just individual web-pages.  Whether that's actually practical fix (and whether Fission will mitigate it), I don't know.

	Dan Mosedale (:dmosedale, :dmose)
	Comment 2 • 5 years ago

I'm putting this in Core:Performance, as I'm guessing that's where stuff like the infobar and it's implementation are handled.