diff --git a/src/schematics/add/index.ts b/src/schematics/add/index.ts
index 150be7c40..2a9c926ec 100644
--- a/src/schematics/add/index.ts
+++ b/src/schematics/add/index.ts
@@ -1,6 +1,6 @@
 import { SchematicContext, Tree } from '@angular-devkit/schematics';
 import { NodePackageInstallTask, RunSchematicTask } from '@angular-devkit/schematics/tasks';
-import { addDependencies } from '../common';
+import { addDependencies, pinInstalledPrereleaseVersion } from '../common';
 import { DeployOptions } from '../interfaces';
 import { peerDependencies } from '../versions.json';
 
@@ -10,6 +10,7 @@ export const ngAdd = (options: DeployOptions) => (tree: Tree, context: Schematic
     peerDependencies,
     context
   );
+  pinInstalledPrereleaseVersion(tree, context);
   const npmInstallTaskId = context.addTask(new NodePackageInstallTask());
   context.addTask(new RunSchematicTask('ng-add-setup-project', options), [npmInstallTaskId]);
   return tree;
diff --git a/src/schematics/common.jasmine.ts b/src/schematics/common.jasmine.ts
new file mode 100644
index 000000000..b40612d04
--- /dev/null
+++ b/src/schematics/common.jasmine.ts
@@ -0,0 +1,117 @@
+import { logging } from '@angular-devkit/core';
+import { HostTree, SchematicContext } from '@angular-devkit/schematics';
+import { pinInstalledPrereleaseVersion } from './common.js';
+import 'jasmine';
+
+const context = { logger: new logging.Logger('test') } as unknown as SchematicContext;
+
+const treeWithAngularFire = (declaredVersion: string, section = 'dependencies') => {
+  const tree = new HostTree();
+  tree.create('package.json', JSON.stringify({
+    name: 'test-app',
+    [section]: {
+      '@angular/fire': declaredVersion,
+      firebase: '^12.4.0',
+    },
+  }, null, 2));
+  return tree;
+};
+
+const sectionIn = (tree: HostTree, section: string) =>
+  JSON.parse(tree.readText('package.json'))[section];
+
+const dependenciesIn = (tree: HostTree) => sectionIn(tree, 'dependencies');
+
+describe('pinInstalledPrereleaseVersion', () => {
+
+  it('pins a caret prerelease range to the exact installed version', () => {
+    const tree = treeWithAngularFire('^21.0.0-rc.0');
+    pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0');
+    expect(dependenciesIn(tree)['@angular/fire']).toBe('21.0.0-rc.0');
+  });
+
+  it('pins a tilde prerelease range to the exact installed version', () => {
+    const tree = treeWithAngularFire('~21.0.0-rc.0');
+    pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0');
+    expect(dependenciesIn(tree)['@angular/fire']).toBe('21.0.0-rc.0');
+  });
+
+  it('leaves other dependencies untouched when pinning', () => {
+    const tree = treeWithAngularFire('^21.0.0-rc.0');
+    pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0');
+    expect(dependenciesIn(tree).firebase).toBe('^12.4.0');
+  });
+
+  it('leaves a stable caret range untouched', () => {
+    const tree = treeWithAngularFire('^21.0.0');
+    pinInstalledPrereleaseVersion(tree, context, '21.0.0');
+    expect(dependenciesIn(tree)['@angular/fire']).toBe('^21.0.0');
+  });
+
+  it('leaves an exact prerelease version untouched', () => {
+    const tree = treeWithAngularFire('21.0.0-rc.0');
+    pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0');
+    expect(dependenciesIn(tree)['@angular/fire']).toBe('21.0.0-rc.0');
+  });
+
+  it('leaves a hand-authored range expression untouched', () => {
+    const tree = treeWithAngularFire('>=21.0.0-rc.0');
+    pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0');
+    expect(dependenciesIn(tree)['@angular/fire']).toBe('>=21.0.0-rc.0');
+  });
+
+  it('does not pin when the installed version does not satisfy the declared range', () => {
+    const tree = treeWithAngularFire('^21.0.0-rc.0');
+    pinInstalledPrereleaseVersion(tree, context, '22.0.0-rc.0');
+    expect(dependenciesIn(tree)['@angular/fire']).toBe('^21.0.0-rc.0');
+  });
+
+  it('warns and does not pin when the installed version is not valid semver', () => {
+    const warnSpy = spyOn(context.logger, 'warn');
+    const tree = treeWithAngularFire('^21.0.0-rc.0');
+    pinInstalledPrereleaseVersion(tree, context, 'ANGULARFIRE2_VERSION');
+    expect(warnSpy).toHaveBeenCalled();
+    expect(dependenciesIn(tree)['@angular/fire']).toBe('^21.0.0-rc.0');
+  });
+
+  it('does nothing when the @angular/fire entry is not a string', () => {
+    const tree = new HostTree();
+    tree.create('package.json', JSON.stringify({
+      name: 'test-app',
+      dependencies: { '@angular/fire': { version: '^21.0.0-rc.0' } },
+    }));
+    expect(() => pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0')).not.toThrow();
+    expect(dependenciesIn(tree)['@angular/fire']).toEqual({ version: '^21.0.0-rc.0' });
+  });
+
+  it('does nothing when @angular/fire is not a dependency', () => {
+    const tree = new HostTree();
+    tree.create('package.json', JSON.stringify({ name: 'test-app', dependencies: {} }));
+    expect(() => pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0')).not.toThrow();
+    expect(dependenciesIn(tree)['@angular/fire']).toBeUndefined();
+  });
+
+  it('does nothing when package.json is absent', () => {
+    const tree = new HostTree();
+    expect(() => pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0')).not.toThrow();
+  });
+
+  it('pins a prerelease range found in devDependencies', () => {
+    const tree = treeWithAngularFire('^21.0.0-rc.0', 'devDependencies');
+    pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0');
+    expect(sectionIn(tree, 'devDependencies')['@angular/fire']).toBe('21.0.0-rc.0');
+  });
+
+  it('pins the dependencies entry when @angular/fire appears in both sections', () => {
+    const tree = new HostTree();
+    tree.create('package.json', JSON.stringify({
+      name: 'test-app',
+      dependencies: { '@angular/fire': '^21.0.0-rc.0' },
+      devDependencies: { '@angular/fire': '^21.0.0-rc.0' },
+    }, null, 2));
+    pinInstalledPrereleaseVersion(tree, context, '21.0.0-rc.0');
+    expect(dependenciesIn(tree)['@angular/fire']).toBe('21.0.0-rc.0');
+    expect(sectionIn(tree, 'devDependencies')['@angular/fire']).toBe('^21.0.0-rc.0');
+  });
+
+});
diff --git a/src/schematics/common.ts b/src/schematics/common.ts
index 9f3544efc..525440321 100644
--- a/src/schematics/common.ts
+++ b/src/schematics/common.ts
@@ -1,5 +1,10 @@
 import { SchematicContext, SchematicsException, Tree } from '@angular-devkit/schematics';
-import { intersects as semverIntersects } from 'semver';
+import {
+  intersects as semverIntersects,
+  prerelease as semverPrerelease,
+  satisfies as semverSatisfies,
+  valid as semverValid,
+} from 'semver';
 import { FirebaseHostingSite } from './interfaces';
 
 export const shortSiteName = (site?: FirebaseHostingSite) => site?.name?.split('/').pop();
@@ -65,3 +70,50 @@ export const addDependencies = (
 
   overwriteIfExists(host, 'package.json', stringifyFormatted(packageJson));
 };
+
+// The build writes the published version over this placeholder in the compiled schematics
+// (tools/build.ts, replaceSchematicVersions); running from source leaves the placeholder.
+const angularFireVersion = 'ANGULARFIRE2_VERSION';
+
+/**
+ * Pins the workspace's `@angular/fire` entry to the exact installed version when `ng add` wrote a
+ * prerelease range. A prerelease range like `^21.0.0-rc.0` also matches the canary build published
+ * for every merge to main, so a later fresh install can silently replace the version the user
+ * chose. Stable ranges are left untouched.
+ */
+export const pinInstalledPrereleaseVersion = (
+  host: Tree,
+  context: SchematicContext,
+  installedVersion = angularFireVersion,
+) => {
+  if (!host.exists('package.json')) { return; }
+  const packageJson = safeReadJSON('package.json', host);
+
+  const dependencySection = ['dependencies', 'devDependencies'].find(
+    section => typeof packageJson[section]?.['@angular/fire'] === 'string',
+  );
+  if (!dependencySection) { return; }
+
+  const declaredAngularFireVersion = packageJson[dependencySection]['@angular/fire'];
+  if (!(declaredAngularFireVersion.startsWith('^') || declaredAngularFireVersion.startsWith('~'))) { return; }
+
+  if (!semverValid(installedVersion)) {
+    context.logger.warn(
+      'Could not determine the installed @angular/fire version; leaving the declared version range as-is.'
+    );
+    return;
+  }
+
+  if (
+    semverPrerelease(installedVersion) &&
+    semverSatisfies(installedVersion, declaredAngularFireVersion, { includePrerelease: true })
+  ) {
+    packageJson[dependencySection]['@angular/fire'] = installedVersion;
+    overwriteIfExists(host, 'package.json', stringifyFormatted(packageJson));
+    context.logger.info(
+      `Pinned @angular/fire to the exact version ${installedVersion} — a prerelease range like ` +
+      `${declaredAngularFireVersion} also matches unreviewed canary builds, so a later install ` +
+      'could silently change versions.'
+    );
+  }
+};
diff --git a/tools/build.ts b/tools/build.ts
index 8152ab59d..0e66812e1 100644
--- a/tools/build.ts
+++ b/tools/build.ts
@@ -1,6 +1,6 @@
 import { spawn } from 'cross-spawn';
 import { copy, writeFile } from 'fs-extra';
-import { join } from 'path';
+import { join, sep } from 'path';
 import { keys as tsKeys } from 'ts-transformer-keys';
 import * as esbuild from "esbuild";
 
@@ -273,6 +273,21 @@ async function replacePackageCoreVersion() {
   });
 }
 
+async function writeVersionOverPlaceholder(root: { version: string }) {
+  const replace = require('replace-in-file');
+  const replacements = await replace({
+    // Glob patterns need forward slashes even on Windows.
+    files: `${dest('schematics').split(sep).join('/')}/**/*.js`,
+    from: /ANGULARFIRE2_VERSION/g,
+    to: root.version,
+    // Zero matches should reach the guard below, not replace-in-file's generic rejection.
+    allowEmptyPaths: true,
+  });
+  if (!replacements.some(replacement => replacement.hasChanged)) {
+    throw new Error('No ANGULARFIRE2_VERSION placeholder found in the compiled schematics — the version pin would ship disabled.');
+  }
+}
+
 async function replaceSchematicVersions() {
   const root = await rootPackage;
   const packagesPath = dest('schematics', 'versions.json');
@@ -283,6 +298,7 @@ async function replaceSchematicVersions() {
   Object.keys(dependencies.firebaseFunctionsDependencies).forEach(name => {
     dependencies.firebaseFunctionsDependencies[name].version = root.dependencies[name] || root.devDependencies[name];
   });
+  await writeVersionOverPlaceholder(root);
   return writeFile(packagesPath, JSON.stringify(dependencies, null, 2));
 }