1798500 - Setting pref accessibility.force-disabled to -1 does not appear to enable accessibility on Linux

Status: RESOLVED FIXED

(Core :: Disability Access APIs, defect, P1)

Description

[Jason Kratzer [:jkratzer]]

We recently replaced GNOME_ACCESSIBILITY=1 on linux with user_pref("accessibility.force_disabled", -1) and noticed that accessibility coverage dropped to near 0. After speaking with :jteh, it appears that this pref is not working as expected.

Comment 1

[James Teh [:Jamie]]

I'm actually starting to think this doesn't work on any platform other than Mac... and I don't even understand how it works there.

Eitan, how does this work on Mac? I see that ShouldA11yBeEnabled supports this and I see that ShouldA11yBeEnabled gets called in various places when the platform requests something on an Accessible. However, that still requires the platform to send some query before we create the AccService. The force enable just says we don't need to worry about AXEnhancedUserInterface. Does Mac just always send a11y queries or something?

Comment 2

[James Teh [:Jamie]]

Copying Morgan and Nathan as well, since they might be surprised to learn that this pref doesn't actually work the way we think it does... or alternatively, they might be able to point out something I'm missing. :(

Comment 3

[Nathan LaPré]

My recent testing of the Windows hang incident suggests to me that setting this pref in about:config is definitely working on Windows. This is probably my inexperience talking, but are we talking about doing this from about:config or starting the browser with --setpref="accessibility.force_disabled=-1", or something else?

Comment 4

[James Teh [:Jamie]]

(In reply to Nathan LaPré from comment #3)

My recent testing of the Windows hang incident suggests to me that setting this pref in about:config is definitely working on Windows.

That's helpful, thanks. Given that, plus something I just vaguely recalled seeing years ago, I finally found where we do this on Windows:
https://searchfox.org/mozilla-central/rev/aa1bb4f0ca8bfda4b117d1befca47b72d5dd6d5d/widget/windows/nsWindow.cpp#1235
This was implemented in bug 1342245. I was looking for a call to PlatformDisabledState, but the Windows widget code reads the pref directly. Urgh.

I also don't understand why we do this differently on every platform instead of creating the a11y service in some cross-platform way if it is force enabled. For Windows, bug 1342245 has this to say:

The post message bounce works around a lack of initialization for some objects checked in the GetAccessible code.

Unfortunately, I don't know which "some objects" had a "lack of initialization", so that's not super helpful.

This is probably my inexperience talking, but are we talking about doing this from about:config or starting the browser with --setpref="accessibility.force_disabled=-1", or something else?

Any way of setting a pref at startup.

Comment 5

[James Teh [:Jamie]]

Fixing this on Linux should be pretty straightforward. Ideally, I think this should be implemented in a cross-platform way, but that's going to require more investigation/thought, so let's deal with the problem at hand for now.

Comment 6

[James Teh [:Jamie]]

Attachment: Bug 1798500: Support accessibility.force_disabled=-1 for ATK.

Comment 7

[Morgan Reschenberg [:morgan]]

(In reply to James Teh [:Jamie] from comment #4)

(In reply to Nathan LaPré from comment #3)

This is probably my inexperience talking, but are we talking about doing this from about:config or starting the browser with --setpref="accessibility.force_disabled=-1", or something else?

Any way of setting a pref at startup.

FWIW on mac you can change this dynamically without restart

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/28ca3769b1d4
Support accessibility.force_disabled=-1 for ATK. r=eeejay

Comment 9

[Serban Stanca [:SerbanS]]

https://hg.mozilla.org/mozilla-central/rev/28ca3769b1d4