diff --git a/README.md b/README.md
index f4d082b92..08098b12d 100644
--- a/README.md
+++ b/README.md
@@ -211,6 +211,8 @@ In order to build successfully, you need to check out a commit in the dependency
 - Run the `<android-components>/tools/list_compatible_dependency_versions.py` script to output a compatible commit
 - Check out the latest commit from main in this repository and the dependency repository. However, this may fail if there were breaking changes added recently to the dependency.
 
+If you're trying to build fenix with a local ac AND a local GV, you'll have to use another method: see [this doc](https://github.com/mozilla-mobile/fenix/blob/main/docs/substituting-local-ac-and-gv.md).
+
 ### Using Nimbus servers during local development
 If you're working with the Nimbus experiments platform, by default for local development Fenix configures Nimbus to not use a server.
 
diff --git a/docs/substituting-local-ac-and-gv.md b/docs/substituting-local-ac-and-gv.md
new file mode 100644
index 000000000..dc999a911
--- /dev/null
+++ b/docs/substituting-local-ac-and-gv.md
@@ -0,0 +1,101 @@
+# Substituting local ac and GV
+To build fenix with a local android-components or local GeckoView, we recommend the following methods:
+
+|type|fenix -> local ac|fenix -> local GV|fenix -> local ac -> local GV|
+|-|-|-|-|
+|**method**|local.properties|local.properties|manual publish + local.properties|
+
+For instructions with `local.properties`, see [the root README](https://github.com/mozilla-mobile/fenix/blob/main/README.md). For instructions on manual publish + local.properties, keep reading. See [ac#8386](https://github.com/mozilla-mobile/android-components/issues/8386) for why we can't use local properties for fenix -> local ac -> local GV publishing.
+
+## fenix -> local ac -> local GV
+We're going to manually publish our GeckoView to our local maven repository, modify ac locally to consume it, and use local.properties to build fenix -> local ac.
+
+### 1. Synchronize checkouts
+To avoid breaking changes causing our builds to fail, we should make sure each of the repositories is on a commit from around the same time frame. You can use the [`android-components/tools/list_compatible_dependency_versions.py` script](https://github.com/mozilla-mobile/android-components/blob/main/tools/list_compatible_dependency_versions.py) to trivially identify ac and GV builds from a given fenix commit. If you want to synchronize builds from a GV or ac commit, you'll likely need to try to align around the commit merge dates (use `git log --pretty=fuller`).
+
+### 2. Manually publish GeckoView
+With our builds synchronized, we can publish our local changes to GeckoView. To publish GeckoView, run:
+```sh
+./mach build && ./mach gradle \
+    geckoview:publishWithGeckoBinariesDebugPublicationToMavenLocal \
+    exoplayer2:publishDebugPublicationToMavenLocal
+```
+
+This **needs to be run every time you make changes.**
+
+We also need to know what version of GeckoView we published. You can make this local change:
+```diff
+diff --git a/mobile/android/geckoview/build.gradle b/mobile/android/geckoview/build.gradle
+--- a/mobile/android/geckoview/build.gradle
++++ b/mobile/android/geckoview/build.gradle
+@@ -382,16 +382,17 @@ android.libraryVariants.all { variant ->
+     // and we can simply extend its inputs.  See
+     // https://android.googlesource.com/platform/tools/base/+/0cbe8846f7d02c0bb6f07156b9f4fde16d96d329/build-system/gradle-core/src/main/java/com/android/build/gradle/tasks/BundleAar.kt#94.
+     variant.packageLibraryProvider.get().from("${topsrcdir}/toolkit/components/telemetry/geckoview/streaming/metrics.yaml")
+ }
+
+ apply plugin: 'maven-publish'
+
+ version = getVersionNumber()
++println("version = " + version)
+ group = 'org.mozilla.geckoview'
+
+ def getArtifactId() {
+     def id = "geckoview" + project.ext.artifactSuffix
+
+     if (!mozconfig.substs.MOZ_ANDROID_GECKOVIEW_LITE) {
+         id += "-omni"
+     }
+```
+
+And execute `./mach build | grep version` to find a version number like `98.0.20211208151112-SNAPSHOT`.
+
+### 3. Modify ac to consume local GV
+See the diff below. Remember to update the GV version with the version you found in step 2!
+```diff
+diff --git a/build.gradle b/build.gradle
+index fa8149781f..863df65a57 100644
+--- a/build.gradle
++++ b/build.gradle
+@@ -6,6 +6,7 @@ import static org.gradle.api.tasks.testing.TestResult.ResultType
+
+ buildscript {
+     repositories {
++        mavenLocal()
+         if (project.hasProperty("googleRepo")) {
+             maven {
+                 name "Google"
+@@ -40,6 +41,7 @@ plugins {
+
+ allprojects {
+     repositories {
++        mavenLocal()
+         if (project.hasProperty("googleRepo")) {
+             maven {
+                 name "Google"
+diff --git a/buildSrc/src/main/java/Gecko.kt b/buildSrc/src/main/java/Gecko.kt
+index 331158bf50..f37a05791a 100644
+--- a/buildSrc/src/main/java/Gecko.kt
++++ b/buildSrc/src/main/java/Gecko.kt
+@@ -9,7 +9,10 @@ object Gecko {
+     /**
+      * GeckoView Version.
+      */
+-    const val version = "98.0.20220125100058"
++    const val version = "98.0.20211208151112-SNAPSHOT"
+
+     /**
+      * GeckoView channel
+@@ -23,7 +26,7 @@ object Gecko {
+ enum class GeckoChannel(
+     val artifactName: String
+ ) {
+-    NIGHTLY("geckoview-nightly-omni"),
++    NIGHTLY("geckoview-default-omni"),
+     BETA("geckoview-beta-omni"),
+     RELEASE("geckoview-omni")
+ }
+```
+
+### 4. Build fenix with local.properties change
+Now build fenix as usual with [the `local.properties` change](https://github.com/mozilla-mobile/fenix#auto-publication-workflow-for-android-components-and-application-services) to build with your local ac. This build will automatically build ac each time it is run. You should have a fenix -> local ac -> local GV build now!