Bug 1956415 part 2: Disable native UIA when JAWS, other Vispero products or NVDA are detected. r=morgan

JAWS and NVDA will continue to use IA2 in Firefox.
However, enabling native UIA in Gecko causes them both to try to use UIA, which causes breakage.
The same is presumably true for other Vispero products, as they use components shared with JAWS.
Future versions of these products will handle this correctly themselves.
Until then, disable UIA when these products are detected.

As part of this, the UIA pref has been changed from a bool to a uint32_t.
This will cause existing configurations of this pref to be reset to the default, but this is okay because this pref has never been documented, exposed in the UI or intended for public usage.
This allows for three values: 0 to never enable, 1 to always enable and 2 to enable unless incompatible clients are detected.
This makes it possible for developers to test those clients with Gecko's UIA implementation when necessary.

Differential Revision: https://phabricator.services.mozilla.com/D243245

Author: jcsteh

accessible/tests/browser/windows/uia/head.js

@@ -38,7 +38,7 @@ function addUiaTask(doc, task, options = {}) {
   function addTask(shouldEnable) {
     async function uiaTask(browser, docAcc, topDocAcc) {
       await SpecialPowers.pushPrefEnv({
-        set: [["accessibility.uia.enable", shouldEnable]],
+        set: [["accessibility.uia.enable", shouldEnable ? 2 : 0]],
       });
       gIsUiaEnabled = shouldEnable;
       info(shouldEnable ? "Gecko UIA enabled" : "Gecko UIA disabled");

accessible/windows/msaa/Compatibility.cpp

@@ -218,5 +218,16 @@ SuppressionReasons Compatibility::A11ySuppressionReasons() {
 /* static */
 bool Compatibility::IsUiaEnabled() {
   // This is the only function which should call the UIA pref function directly.
-  return StaticPrefs::accessibility_uia_enable_DoNotUseDirectly();
+  const uint32_t pref =
+      StaticPrefs::accessibility_uia_enable_DoNotUseDirectly();
+  if (pref == 0) {
+    return false;  // Never enable.
+  }
+  if (pref == 1) {
+    return true;  // Always enable.
+  }
+  // Bug 1956415: Some screen readers break when native UIA is enabled, so don't
+  // enable it when they're detected.
+  return !IsJAWS() && !IsOldJAWS() && !IsVisperoShared() &&
+         !(sConsumers & NVDA);
 }

modules/libpref/init/StaticPrefList.yaml

@@ -288,10 +288,13 @@
 #endif
   mirror: always
 
-# Whether to enable support for the UI Automation API on Windows.
+# Whether to enable support for the UI Automation API on Windows. Values:
+# * 0: Never.
+# * 1: Always.
+# * 2: Enable unless incompatible accessibility clients are detected.
 - name: accessibility.uia.enable
-  type: bool
-  value: false
+  type: uint32_t
+  value: 0
   mirror: always
   do_not_use_directly: true