--- a/toolkit/mozapps/extensions/internal/XPIInstall.jsm
+++ b/toolkit/mozapps/extensions/internal/XPIInstall.jsm
@@ -1794,33 +1794,38 @@ class AddonInstall {
                                                  this.listeners, this.wrapper,
                                                  this.addon.wrapper);
       } else {
         // The install is completed so it should be removed from the active list
         XPIProvider.removeActiveInstall(this);
 
         // Deactivate and remove the old add-on as necessary
         let reason = BOOTSTRAP_REASONS.ADDON_INSTALL;
+        let callUpdate = false;
         if (this.existingAddon) {
           if (Services.vc.compare(this.existingAddon.version, this.addon.version) < 0)
             reason = BOOTSTRAP_REASONS.ADDON_UPGRADE;
           else
             reason = BOOTSTRAP_REASONS.ADDON_DOWNGRADE;
 
+          callUpdate = isWebExtension(this.addon.type) && isWebExtension(this.existingAddon.type);
+
           if (this.existingAddon.bootstrap) {
             let file = this.existingAddon._sourceBundle;
             if (this.existingAddon.active) {
               XPIProvider.callBootstrapMethod(this.existingAddon, file,
                                               "shutdown", reason,
                                               { newVersion: this.addon.version });
             }
 
-            XPIProvider.callBootstrapMethod(this.existingAddon, file,
-                                            "uninstall", reason,
-                                            { newVersion: this.addon.version });
+            if (!callUpdate) {
+              XPIProvider.callBootstrapMethod(this.existingAddon, file,
+                                              "uninstall", reason,
+                                              { newVersion: this.addon.version });
+            }
             XPIProvider.unloadBootstrapScope(this.existingAddon.id);
             flushChromeCaches();
           }
 
           if (!isUpgrade && this.existingAddon.active) {
             XPIDatabase.updateAddonActive(this.existingAddon, false);
           }
         }
@@ -1856,17 +1861,18 @@ class AddonInstall {
         XPIStates.save();
 
         let extraParams = {};
         if (this.existingAddon) {
           extraParams.oldVersion = this.existingAddon.version;
         }
 
         if (this.addon.bootstrap) {
-          XPIProvider.callBootstrapMethod(this.addon, file, "install",
+          let method = callUpdate ? "update" : "install";
+          XPIProvider.callBootstrapMethod(this.addon, file, method,
                                           reason, extraParams);
         }
 
         AddonManagerPrivate.callAddonListeners("onInstalled",
                                                this.addon.wrapper);
 
         logger.debug("Install of " + this.sourceURI.spec + " completed.");
         this.state = AddonManager.STATE_INSTALLED;

--- a/toolkit/mozapps/extensions/internal/XPIProvider.jsm
+++ b/toolkit/mozapps/extensions/internal/XPIProvider.jsm
@@ -2387,33 +2387,38 @@ this.XPIProvider = {
     let tempLocation = XPIStates.getLocation(TemporaryInstallLocation.name);
     if (tempLocation) {
       for (let [id, addon] of tempLocation.entries()) {
         tempLocation.delete(id);
 
         let reason = BOOTSTRAP_REASONS.ADDON_UNINSTALL;
 
         let existing = XPIStates.findAddon(id, loc => loc != tempLocation);
+        let callUpdate = false;
         if (existing) {
           reason = newVersionReason(addon.version, existing.version);
+          callUpdate = (isWebExtension(addon.type) && isWebExtension(existing.type));
         }
 
         this.callBootstrapMethod(addon, addon.file, "shutdown", reason);
-        this.callBootstrapMethod(addon, addon.file, "uninstall", reason);
+        if (!callUpdate) {
+          this.callBootstrapMethod(addon, addon.file, "uninstall", reason);
+        }
         this.unloadBootstrapScope(id);
         TemporaryInstallLocation.uninstallAddon(id);
         XPIStates.removeAddon(TemporaryInstallLocation.name, id);
 
         if (existing) {
           let newAddon = XPIDatabase.makeAddonLocationVisible(id, existing.location.name);
 
           let file = new nsIFile(newAddon.path);
 
           let data = {oldVersion: addon.version};
-          this.callBootstrapMethod(newAddon, file, "install", reason, data);
+          let method = callUpdate ? "update" : "install";
+          this.callBootstrapMethod(newAddon, file, method, reason, data);
         }
       }
     }
   },
 
   /**
    * Applies any pending theme change to the preferences.
    */
@@ -3548,16 +3553,17 @@ this.XPIProvider = {
 
     if (!addon.bootstrap) {
       throw new Error("Only restartless (bootstrap) add-ons"
                     + " can be installed from sources:", addon.id);
     }
     let installReason = BOOTSTRAP_REASONS.ADDON_INSTALL;
     let oldAddon = await new Promise(
                    resolve => XPIDatabase.getVisibleAddonForID(addon.id, resolve));
+    let callUpdate = false;
 
     let extraParams = {};
     extraParams.temporarilyInstalled = aInstallLocation === TemporaryInstallLocation;
     if (oldAddon) {
       if (!oldAddon.bootstrap) {
         logger.warn("Non-restartless Add-on is already installed", addon.id);
         throw new Error("Non-restartless add-on with ID "
                         + oldAddon.id + " is already installed");
@@ -3576,34 +3582,40 @@ this.XPIProvider = {
         let oldVersion = oldAddon.version;
 
         installReason = newVersionReason(oldVersion, newVersion);
         let uninstallReason = installReason;
 
         extraParams.newVersion = newVersion;
         extraParams.oldVersion = oldVersion;
 
+        callUpdate = isWebExtension(oldAddon.type) && isWebExtension(addon.type);
+
         if (oldAddon.active) {
           XPIProvider.callBootstrapMethod(oldAddon, existingAddon,
                                           "shutdown", uninstallReason,
                                           extraParams);
         }
-        this.callBootstrapMethod(oldAddon, existingAddon,
-                                 "uninstall", uninstallReason, extraParams);
+
+        if (!callUpdate) {
+          this.callBootstrapMethod(oldAddon, existingAddon,
+                                   "uninstall", uninstallReason, extraParams);
+        }
         this.unloadBootstrapScope(existingAddonID);
         flushChromeCaches();
       }
     } else {
       addon.installDate = Date.now();
     }
 
     let file = addon._sourceBundle;
 
     XPIProvider._addURIMapping(addon.id, file);
-    XPIProvider.callBootstrapMethod(addon, file, "install", installReason, extraParams);
+    let method = callUpdate ? "update" : "install";
+    XPIProvider.callBootstrapMethod(addon, file, method, installReason, extraParams);
     addon.state = AddonManager.STATE_INSTALLED;
     logger.debug("Install of temporary addon in " + aFile.path + " completed.");
     addon.visible = true;
     addon.enabled = true;
     addon.active = true;
     // WebExtension themes are installed as disabled, fix that here.
     addon.userDisabled = false;
 
@@ -4648,31 +4660,35 @@ this.XPIProvider = {
       // strange as in some cases this operation can complete without a restart
       // so really this is now saying that the uninstall isn't going to happen
       // immediately but will happen later.
       AddonManagerPrivate.callAddonListeners("onUninstalling", wrapper,
                                              makePending);
     }
 
     let reason = BOOTSTRAP_REASONS.ADDON_UNINSTALL;
+    let callUpdate = false;
     let existingAddon = XPIStates.findAddon(aAddon.id, loc =>
       loc.name != aAddon._installLocation.name);
     if (existingAddon) {
       reason = newVersionReason(aAddon.version, existingAddon.version);
+      callUpdate = isWebExtension(aAddon.type) && isWebExtension(existingAddon.type);
     }
 
     if (!makePending) {
       if (aAddon.bootstrap) {
         if (aAddon.active) {
           this.callBootstrapMethod(aAddon, aAddon._sourceBundle, "shutdown",
                                    reason);
         }
 
-        this.callBootstrapMethod(aAddon, aAddon._sourceBundle, "uninstall",
-                                 reason);
+        if (!callUpdate) {
+          this.callBootstrapMethod(aAddon, aAddon._sourceBundle, "uninstall",
+                                   reason);
+        }
         XPIStates.disableAddon(aAddon.id);
         this.unloadBootstrapScope(aAddon.id);
         flushChromeCaches();
       }
       aAddon._installLocation.uninstallAddon(aAddon.id);
       XPIDatabase.removeAddonMetadata(aAddon);
       XPIStates.removeAddon(aAddon.location, aAddon.id);
       AddonManagerPrivate.callAddonListeners("onUninstalled", wrapper);
@@ -4684,18 +4700,19 @@ this.XPIProvider = {
           let wrappedAddon = existing.wrapper;
           AddonManagerPrivate.callAddonListeners("onInstalling", wrappedAddon, false);
 
           if (!existing.disabled && !XPIProvider.enableRequiresRestart(existing)) {
             XPIDatabase.updateAddonActive(existing, true);
           }
 
           if (aAddon.bootstrap) {
+            let method = callUpdate ? "update" : "install";
             XPIProvider.callBootstrapMethod(existing, existing._sourceBundle,
-                                            "install", reason);
+                                            method, reason);
 
             if (existing.active) {
               XPIProvider.callBootstrapMethod(existing, existing._sourceBundle,
                                               "startup", reason);
             } else {
               XPIProvider.unloadBootstrapScope(existing.id);
             }
           }