--- a/browser/base/content/test/favicons/accept.sjs
+++ b/browser/base/content/test/favicons/accept.sjs
@@ -1,15 +1,15 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/
  */
 
 function handleRequest(request, response) {
   // Doesn't seem any way to get the value from prefs from here. :(
-  let expected = "image/webp,*/*";
+  let expected = "image/avif,image/webp,*/*";
   if (expected != request.getHeader("Accept")) {
     response.setStatusLine(request.httpVersion, 404, "Not Found");
     return;
   }
 
   response.setStatusLine(request.httpVersion, 302, "Moved Temporarily");
   response.setHeader("Location", "moz.png");
 }

--- a/browser/components/preferences/tests/head.js
+++ b/browser/components/preferences/tests/head.js
@@ -192,17 +192,17 @@ class DefinitionServer {
     const { primaryScheme, primaryHost, primaryPort } = this.server.identity;
     return `${primaryScheme}://${primaryHost}:${primaryPort}/definitions.json`;
   }
 
   addDefinition(overrides = {}) {
     const definition = {
       id: "test-feature",
       // These l10n IDs are just random so we have some text to display
-      title: "experimental-features-media-avif",
+      title: "experimental-features-media-jxl",
       description: "pane-experimental-description2",
       restartRequired: false,
       type: "boolean",
       preference: "test.feature",
       defaultValue: false,
       isPublic: false,
       ...overrides,
     };

--- a/devtools/client/netmonitor/test/browser_net_copy_headers.js
+++ b/devtools/client/netmonitor/test/browser_net_copy_headers.js
@@ -37,17 +37,17 @@ add_task(async function() {
 
   const selectedRequest = getSelectedRequest(store.getState());
   is(selectedRequest, requestItem, "Proper request is selected");
 
   const EXPECTED_REQUEST_HEADERS = [
     `${method} ${SIMPLE_URL} ${httpVersion}`,
     "Host: example.com",
     "User-Agent: " + navigator.userAgent + "",
-    "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
+    "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8",
     "Accept-Language: " + navigator.languages.join(",") + ";q=0.5",
     "Accept-Encoding: gzip, deflate",
     "Connection: keep-alive",
     "Upgrade-Insecure-Requests: 1",
     "Pragma: no-cache",
     "Cache-Control: no-cache",
   ].join("\n");
 

--- a/image/test/mochitest/bug496292-1.sjs
+++ b/image/test/mochitest/bug496292-1.sjs
@@ -4,17 +4,17 @@ function handleRequest(request, response
              .getService(Components.interfaces.nsIProperties)
              .get("CurWorkD", Components.interfaces.nsIFile);
 
   file.append("tests");
   file.append("image");
   file.append("test");
   file.append("mochitest");
 
-  if (request.getHeader("Accept") == "image/webp,*/*") {
+  if (request.getHeader("Accept") == "image/avif,image/webp,*/*") {
     file.append('blue.png');
   } else {
     file.append('red.png');
   }
   response.setStatusLine(request.httpVersion, 200, "OK");
   response.setHeader("Content-Type", "image/png", false);
   response.setHeader("Cache-Control", "no-cache", false);
 

--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -5633,17 +5633,17 @@
   type: RelaxedAtomicBool
   value: true
   mirror: always
 
 # Whether we attempt to decode AVIF images or not.
 - name: image.avif.enabled
   type: RelaxedAtomicBool
 #if defined(MOZ_AV1)
-  value: false
+  value: true
 #else
   value: false
 #endif
   mirror: always
 
 # How strict we are in accepting/rejecting AVIF inputs according to whether they
 # conform to the specification
 # 0 = Permissive: accept whatever we can simply, unambiguously interpret

--- a/netwerk/test/mochitests/test_accept_header.html
+++ b/netwerk/test/mochitests/test_accept_header.html
@@ -21,27 +21,27 @@ function test_last_request_and_continue(
     next();
   });
 }
 
 function test_iframe() {
   let ifr = document.createElement("iframe");
   ifr.src = "test_accept_header.sjs?iframe";
   ifr.onload = () => {
-    test_last_request_and_continue("iframe", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
+    test_last_request_and_continue("iframe", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8");
   };
   document.body.appendChild(ifr);
 }
 
 function test_image() {
   let i = new Image();
   i.src = "test_accept_header.sjs?image";
   i.onload = function() {
     // Fetch spec says we should have: "image/png,image/svg+xml,image/*;q=0.8,*/*;q=0.5"
-    test_last_request_and_continue("image", "image/webp,*/*");
+    test_last_request_and_continue("image", "image/avif,image/webp,*/*");
   }
 }
 
 function test_style() {
   let head = document.getElementsByTagName("head")[0];
   let link = document.createElement("link");
   link.rel = "stylesheet";
   link.type = "text/css";

--- a/toolkit/components/featuregates/Features.toml
+++ b/toolkit/components/featuregates/Features.toml
@@ -15,27 +15,16 @@ description = "experimental-features-web
 description-links = {wikipedia = "https://en.wikipedia.org/wiki/Graphics%20Processing%20Unit", spec = "https://gpuweb.github.io/gpuweb/", bugzilla = "https://bugzilla.mozilla.org/show_bug.cgi?id=1602129"}
 restart-required = true
 preference = "dom.webgpu.enabled"
 type = "boolean"
 bug-numbers = [1602129]
 is-public = {default = false, nightly = true}
 default-value = false
 
-[media-avif]
-title = "experimental-features-media-avif"
-description = "experimental-features-media-avif-description"
-description-links = {bugzilla = "https://bugzilla.mozilla.org/show_bug.cgi?id=1443863"}
-restart-required = false
-preference = "image.avif.enabled"
-type = "boolean"
-bug-numbers = [1443863]
-is-public = {default = false, nightly = true}
-default-value = {default = false, nightly = false}
-
 [media-jxl]
 title = "experimental-features-media-jxl"
 description = "experimental-features-media-jxl-description"
 description-links = {bugzilla = "https://bugzilla.mozilla.org/show_bug.cgi?id=1539075"}
 restart-required = false
 preference = "image.jxl.enabled"
 type = "boolean"
 bug-numbers = [1539075]

--- a/toolkit/locales/en-US/toolkit/featuregates/features.ftl
+++ b/toolkit/locales/en-US/toolkit/featuregates/features.ftl
@@ -11,22 +11,16 @@ experimental-features-css-masonry-descri
 # The title of the experiment should be kept in English as it may be referenced
 # by various online articles and is technical in nature.
 experimental-features-web-gpu2 =
     .label = Web API: WebGPU
 experimental-features-web-gpu-description2 = This new API provides low-level support for performing computation and graphics rendering using the <a data-l10n-name="wikipedia">Graphics Processing Unit (GPU)</a> of the user’s device or computer. The <a data-l10n-name="spec">specification</a> is still a work-in-progress. See <a data-l10n-name="bugzilla">bug 1602129</a> for more details.
 
 # The title of the experiment should be kept in English as it may be referenced
 # by various online articles and is technical in nature.
-experimental-features-media-avif =
-    .label = Media: AVIF
-experimental-features-media-avif-description = With this feature enabled, { -brand-short-name } supports the AV1 Image File (AVIF) format. This is a still image file format that leverages the capabilities of the AV1 video compression algorithms to reduce image size. See <a data-l10n-name="bugzilla">bug 1443863</a> for more details.
-
-# The title of the experiment should be kept in English as it may be referenced
-# by various online articles and is technical in nature.
 experimental-features-media-jxl =
     .label = Media: JPEG XL
 experimental-features-media-jxl-description = With this feature enabled, { -brand-short-name } supports the JPEG XL (JXL) format. This is an enhanced image file format that supports lossless transition from traditional JPEG files. See <a data-l10n-name="bugzilla">bug 1539075</a> for more details.
 
 # The title of the experiment should be kept in English as it may be referenced
 # by various online articles and is technical in nature.
 experimental-features-web-api-inputmode =
     .label = Web API: inputmode