[WebExtensions] Deprecate runtime.PlatformInfo.nacl_arch (#43799)

* [WebExtensions] Deprecate runtime.PlatformInfo.nacl_arch

Chromium is the only engine which supported Google Native Client (NaCl)
and runtime.PlatformInfo.nacl_arch WebExtension API. Chromium removed
NaCl and is currently in the process of removal of associated
WebExtensions API remnants.

Details:
chromium/chromium@913e0c0
chromium/chromium@6e62e12
chromium/chromium@9b22796

* Revert to usual section title

---------

Co-authored-by: rebloor <git@sherpa.co.nz>

Author: bershanskiy

files/en-us/mozilla/add-ons/webextensions/api/runtime/index.md

@@ -26,8 +26,8 @@ It also provides messaging APIs enabling you to:
   - : Identifies the browser's processor architecture.
 - {{WebExtAPIRef("runtime.PlatformInfo")}}
   - : Contains information about the platform the browser is running on.
-- {{WebExtAPIRef("runtime.PlatformNaclArch")}}
-  - : The native client architecture. This may be different from `PlatformArch` on some platforms.
+- {{WebExtAPIRef("runtime.PlatformNaclArch")}} {{deprecated_inline}}
+  - : The deprecated enumeration value representing Google Native Client architecture. Consider migrating to `PlatformArch`, which is supported by Safari and Mozilla, and represents the true CPU architecture and conveys correct bitness information on ARM.
 - {{WebExtAPIRef("runtime.RequestUpdateCheckStatus")}}
   - : Result of a call to {{WebExtAPIRef("runtime.requestUpdateCheck()")}}.
 - {{WebExtAPIRef("runtime.OnInstalledReason")}}

files/en-us/mozilla/add-ons/webextensions/api/runtime/platforminfo/index.md

@@ -16,8 +16,8 @@ Values of this type are objects, which contain the following properties:
   - : {{WebExtAPIRef('runtime.PlatformOs')}}. The platform's operating system.
 - `arch`
   - : {{WebExtAPIRef('runtime.PlatformArch')}}. The platform's processor architecture.
-- `nacl_arch`
-  - : {{WebExtAPIRef('runtime.PlatformNaclArch')}}. The native client architecture. This may be different from `arch` on some platforms.
+- `nacl_arch` {{deprecated_inline}}
+  - : {{WebExtAPIRef('runtime.PlatformNaclArch')}}. The Google Native Client architecture. Only Chromium-based browsers support this attribute, and Chromium is removing it. Consider migrating to `arch`, which contains equivalent information and is more descriptive on some platforms (ARM and RISC-V).
 
 {{WebExtExamples}}
 

files/en-us/mozilla/add-ons/webextensions/api/runtime/platformnaclarch/index.md

@@ -6,11 +6,23 @@ browser-compat: webextensions.api.runtime.PlatformNaclArch
 sidebar: addonsidebar
 ---
 
-The native client architecture. This may be different from arch on some platforms.
+> [!NOTE]
+> **This type is deprecated** in favor of {{WebExtAPIRef("runtime.PlatformArch")}}. `PlatformArch` is also available in {{WebExtAPIRef("runtime.PlatformInfo")}}, which you obtain using {{WebExtAPIRef("runtime.getPlatformInfo()")}}.
+
+The enumerated value representing the CPU instruction set architecture of Google Native Client used by the browser. This enum is deprecated, following the removal of Google Native Client from Google Chrome. As of 2026, Chromium intends to remove this enum.
 
 ## Type
 
-Values of this type are strings. Possible values are: `"arm"`, `"x86-32"`, `"x86-64"`.
+- `ARM`
+  - : The string literal `"arm"`. Represents all versions of the ARM ISA, including all 32-bit and 64-bit variants. Equivalent to [`PlatformArch.arm`](/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/PlatformArch#arm) (32-bit variant) and `PlatformArch.arm64` combined into one value.
+- `X86_32`
+  - : The string literal `"x86-32"`. Represents the 32-bit variant of the x86 architecture. Equivalent to [`PlatformArch.x86_32`](/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/PlatformArch#x86-32).
+- `X86_64`
+  - : The string literal `"x86-64"`. Represents the 64-bit variant of the x86 architecture. Equivalent to [`PlatformArch.X86_64`](/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/PlatformArch#x86-64).
+- `MIPS`
+  - : The string literal `"mips"`. Represents the 32-bit variant of the MIPS ISA, which was never supported by official releases. Equivalent to `PlatformArch.mips`.
+- `MIPS64`
+  - : The string literal `"mips64"`. Represents the 64-bit variant of the MIPS ISA, which was never supported by official releases. Equivalent to `PlatformArch.mips64`.
 
 {{WebExtExamples}}