1266874 - Turn on apz.disable_for_scroll_linked_effects for some portion of the population

Status: RESOLVED WONTFIX

(Core :: Panning and Zooming, defect)

Description

[Kartikaya Gupta (email:[e-mail])]

In an email thread a few weeks ago, Brad said:

> One thing that would make me feel better would be to turn on the code to
> disable APZ for pages with scroll linked events for some set of users so we
> can feel comfortable turning it on if it becomes a problem in beta.

I kind of forgot about this, but better late than never. The code for this landed in bug 1246290 in Gecko 48, with the pref turned off for everybody. We have a few options for turning it on for some users:

1) Add some code to m-c to randomly assign users into a control/experiment group. On first startup with this code, they would have a pref set as to which group they're in, and that pref would persist. Eventually once we decide if we want to turn it off or leave it on, we would land some code that clears out that pref and sets the apz.disable_for_scroll_linked_effects pref appropriately.

2) Basically the same thing, but use the telemetry experiments machinery to accomplish this instead. This approach doesn't require landing any changes in m-c, but we push an experiment that will flip this pref for some portion of the user base.

3) Not sure if this is a possibility, but maybe the e10s system addon that is used for progressive rollout could also flip this pref.

The main goal here is to increase our confidence in a codepath that's disabled by default. So the key is to allow users running that codepath to report issues and make it easy to identify that they are running that codepath. I think both (1) and (2) allow this. Personally I find (1) easier to do because I don't have to jump through all sorts of hoops to do it, and while the code is on Aurora people will get updated pretty frequently so it should be easy enough for us to turn it off.

Comment 1

[Kartikaya Gupta (email:[e-mail])]

There was an email thread discussion and we decided to leave this off for now. We can reconsider it later if we get a lot of reports of badly behaving sites.