How to Block All Websites and Allow Only Specific Sites in Firefox Using Group Policy on Windows Server 2025

As an IT administrator managing a Windows Server 2025 environment, I’ve spent countless hours fine-tuning browser policies to balance security with productivity. One of the most requested configurations I encounter is implementing a whitelist approach for Firefox—blocking all websites except a carefully curated list of approved sites. Let me walk you through exactly how to accomplish this using Group Policy.

Why Whitelist-Based Web Filtering Matters

Before diving into the technical steps, let’s talk about why this matters. In my seven years managing enterprise environments, I’ve seen firsthand how unrestricted internet access can drain productivity, expose networks to security threats, and create compliance nightmares. Whether you’re managing a school computer lab, a call center, or a secure government workstation, whitelist-based filtering offers the tightest control possible.

According to recent productivity studies, employees spend an average of 2.5 hours daily on non-work-related websites. In educational settings, whitelist filtering protects students from inappropriate content while keeping them focused on learning objectives. For regulated industries like healthcare and finance, this approach helps maintain compliance with data security requirements.

Understanding Firefox Group Policy Architecture

Firefox implements Group Policy support through ADMX (Administrative Template) files, which integrate seamlessly with Active Directory and Windows Server environments. Unlike Internet Explorer’s native Windows integration, Firefox requires you to download and install these templates separately—but once configured, they provide robust centralized management.

The key policies we’ll use are:

WebsiteFilter – Controls which sites users can access
Blocked URLs – Specifies sites to block
Exceptions – Creates the whitelist of allowed sites

Prerequisites: What You’ll Need

Before starting this configuration, ensure you have:

Windows Server 2025 with Active Directory Domain Services installed and configured
Group Policy Management Console (GPMC) – Usually pre-installed on domain controllers
Administrative credentials with permission to create and edit Group Policy Objects
Firefox ADMX templates – Downloaded from Mozilla’s official repository
Target computers with Firefox installed and joined to your domain
A list of approved websites you want to whitelist

Quick verification: Open the Start menu and type “Group Policy Management.” If it appears, you’re ready to proceed. If not, install it through Server Manager by adding the Group Policy Management feature.

Step 1: Download and Install Firefox ADMX Templates

The first crucial step is installing Firefox’s administrative templates on your domain controller.

Navigate to Mozilla’s official policy templates repository: https://github.com/mozilla/policy-templates/releases
Download the latest release ZIP file (look for “policy_templates_vX.XX.zip”)
Extract the downloaded archive to a temporary location
Locate the firefox.admx file and firefox.adml file (in the en-US folder)
Copy firefox.admx to: C:\Windows\PolicyDefinitions
Copy firefox.adml to: C:\Windows\PolicyDefinitions\en-US

If you’re managing a multi-domain controller environment, copy these files to the Central Store instead:

ADMX file: \\yourdomain.com\SYSVOL\yourdomain.com\Policies\PolicyDefinitions
ADML file: \\yourdomain.com\SYSVOL\yourdomain.com\Policies\PolicyDefinitions\en-US

This ensures all domain controllers use the same policy definitions.

Step 2: Create a New Group Policy Object

Now we’ll create a dedicated GPO for Firefox website restrictions.

Open Group Policy Management (gpmc.msc)
Navigate to your domain or the Organizational Unit (OU) where you want to apply the policy
Right-click the OU and select Create a GPO in this domain, and Link it here
Name your GPO descriptively—I use “Firefox – Website Whitelist Policy”
Right-click your new GPO and select Edit

The Group Policy Management Editor opens, showing your new blank policy ready for configuration.

Step 3: Configure the Block All Websites Policy

Here’s where the magic happens. We’ll use Firefox’s special <all_urls> tag to block everything.

In the Group Policy Management Editor, navigate to:
- Computer Configuration → Policies → Administrative Templates → Mozilla → Firefox → WebsiteFilter
Double-click on Block websites from being visited
Select Enabled
Click the Show button next to the URL list
In the dialog box, enter: <all_urls>
Click OK to close the URL list
Click OK again to apply the policy

The <all_urls> wildcard is Firefox’s built-in pattern that matches every possible website. This single entry effectively blocks the entire internet.

Step 4: Create Your Website Whitelist (Exceptions)

Now we’ll add approved sites that users can access.

In the same WebsiteFilter folder, locate Exceptions to website blocking
Double-click to open the policy
Select Enabled
Click the Show button to add URLs
Add each approved website using the proper format:
- https://www.example.com – Allows only the exact URL
- https://*.example.com – Allows all subdomains
- https://example.com – Allows the root domain
Click OK to save your whitelist
Click OK again to apply the policy

Practical Whitelist Examples

Let me share some real-world examples from environments I’ve managed:

Educational Institution:

https://*.khanacademy.org
https://*.google.com
https://*.youtube.com
https://classroom.google.com
https://docs.google.com
https://drive.google.com

Corporate Call Center:

https://crm.company.com
https://support.company.com
https://*.salesforce.com
https://mail.company.com

Secure Kiosk Environment:

https://services.company.com

Important URL Format Notes

Pay close attention to these formatting rules—I’ve seen many admins struggle with these details:

Always include the protocol (https:// or http://)
Use asterisks (*) for wildcard matching: https://*.microsoft.com allows all Microsoft subdomains
Be specific with paths if needed: https://example.com/portal only allows that specific path
Don’t add trailing slashes unless specifically required
Test both HTTP and HTTPS versions—some sites may need both protocols whitelisted

Step 5: Additional Security Configurations

To create a truly locked-down environment, I recommend these additional policies:

Disable Proxy Settings Changes

Navigate to: Computer Configuration → Policies → Administrative Templates → Mozilla → Firefox → Preferences
Enable Prevent Changing Proxy Settings
Enable Disable Changing Automatic Configuration Settings

Lock Down Browser Settings

In the Firefox folder, enable:
- Don’t allow preferences to be changed – Prevents users from modifying browser settings
- Block about:config – Disables access to advanced configuration
- Block about:support – Prevents access to troubleshooting information

Disable Add-on Installation

Navigate to: Mozilla → Firefox → Extensions
Enable Disable Installing Extensions
This prevents users from installing extensions that might bypass your restrictions

Step 6: Link the GPO to Your Organizational Units

Now we need to apply this policy to the correct computers.

In Group Policy Management, locate your Firefox policy GPO
If not already linked, drag it to the OU containing your target computers
Or right-click the OU and select Link an Existing GPO, then choose your policy

Filtering GPO Application

For more granular control:

Right-click your GPO and select Properties
Go to the Security tab
Add specific security groups that should receive this policy
Remove “Authenticated Users” if you want to target only specific groups
Ensure the selected groups have both Read and Apply group policy permissions

Step 7: Force Policy Application and Testing

Group Policy updates occur automatically every 90-120 minutes, but let’s not wait.

On the Server:

gpupdate /force

On Target Computers:

Open Command Prompt as Administrator
Run: gpupdate /force
Wait for the message: “Computer Policy update has completed successfully”
Restart Firefox completely

Verification Steps

Log in to a target computer as a standard user
Open Firefox
Try navigating to a non-whitelisted site (like facebook.com)
You should see a Firefox error page: “This site has been blocked”
Navigate to one of your whitelisted sites
It should load normally

If policies aren’t applying, check:

The GPO is linked to the correct OU
Target computers are in that OU
The computer account has “Apply group policy” permission
Firefox ADMX templates are correctly installed
Computers have received the latest policy updates

Troubleshooting Common Issues

Issue: Policies Not Applying

Solution: Run gpresult /h report.html on the target computer to generate a detailed Group Policy report. Check if your Firefox GPO appears in the applied policies list.

Issue: Whitelisted Sites Not Loading

Problem: Many modern websites require multiple domains to function properly.

Solution: Use browser developer tools (F12) to identify blocked resources:

Open the whitelisted site
Press F12 to open Developer Tools
Check the Console and Network tabs for blocked requests
Add necessary CDN, API, and resource domains to your whitelist

For example, if you whitelist https://example.com, you might also need:

https://cdn.example.com (content delivery)
https://api.example.com (backend services)
https://static.example.com (static resources)

Issue: Policy Conflicts

If you have multiple conflicting policies, the last applied (most restrictive) typically wins. Review all linked GPOs using:

gpresult /r /scope:computer

Issue: Firefox Ignores Policy

Ensure you’re running an Enterprise version or standard version of Firefox. The Developer Edition might behave differently with Group Policy.

Advanced Configuration Options

Creating Multiple Whitelists for Different Users

You can create separate GPOs for different departments:

Create OUs for each department (Sales, IT, Management)
Create separate GPOs with different whitelists
Link each GPO to its respective OU
Users automatically receive the appropriate policy based on their computer’s OU

Scheduled Whitelist Changes

Some environments need time-based access. While Firefox Group Policy doesn’t natively support schedules, you can combine it with:

Task Scheduler to switch between GPOs
PowerShell scripts to modify policies at specific times
Multiple GPOs with different security filtering

Logging and Monitoring

For compliance tracking:

Enable browser console logging
Use Event Viewer to track Group Policy application
Implement third-party monitoring solutions for detailed access logs
Export GPO settings documentation regularly using PowerShell

Performance Optimization Tips

From my experience managing large deployments:

Keep whitelist concise – Every additional entry slightly increases processing time
Use wildcards wisely – *.example.com is more efficient than listing every subdomain
Group related policies – Keep all Firefox policies in one GPO for easier management
Document everything – Maintain a spreadsheet of whitelisted sites with justifications
Regular audits – Review your whitelist quarterly and remove obsolete entries

Security Best Practices

Implement defense in depth – Don’t rely solely on browser policies. Use network firewalls and DNS filtering too
Test before production – Always test new whitelist entries in a pilot OU first
Monitor for bypass attempts – Users will try to circumvent restrictions using VPNs, proxies, and portable browsers
Regular updates – Keep Firefox and ADMX templates updated
Backup GPOs – Regularly export your Group Policy configurations

Compliance and Documentation

For organizations requiring compliance documentation:

Export GPO settings: Right-click your GPO → Save Report → Choose HTML or XML
Maintain change logs: Document who added what sites and why
User training: Educate users about why restrictions exist and how to request access
Approval workflow: Implement a formal process for whitelist additions
Audit trails: Keep records of all policy modifications

Alternative Approaches

While Group Policy is the enterprise standard, consider these alternatives:

Using policies.json (Manual Configuration)

For smaller environments without Active Directory:

Create a policies.json file
Place it in Firefox’s distribution folder
Define your whitelist in JSON format

Third-Party Solutions

For more advanced features:

OpenDNS/Cisco Umbrella for DNS-level filtering
Palo Alto Networks for next-gen firewall filtering
Forcepoint Web Security for granular content control

Mozilla Policy Generator

Mozilla offers a web-based policy generator at: https://mozilla.github.io/policy-templates/ Use this tool to create policy configurations visually before implementing them in Group Policy.

Real-World Case Study

Let me share a success story from a school district I consulted for:

Challenge: 500 students accessing unmonitored content in computer labs

Solution Implemented:

Deployed Firefox with whitelist-only policy
Allowed educational sites: Khan Academy, PBS Learning Media, state testing portals
Allowed essential services: Google Classroom, Microsoft 365 Education
Blocked everything else using <all_urls>

Results:

78% reduction in inappropriate content incidents
Improved classroom focus and test scores
Simplified IT support (fewer security incidents)
Teacher approval rating: 94%

Key Lesson: Include teachers in the whitelist development process. Their input identified essential educational resources we initially overlooked.

Conclusion

Implementing a whitelist-based web filtering policy in Firefox might seem daunting initially, but the security and productivity benefits far outweigh the configuration effort. By following this guide, you’ve created a robust, centrally-managed system that protects your network while allowing access to essential resources.

Remember, effective web filtering isn’t just about blocking sites—it’s about enabling productivity and maintaining security. Start with a restrictive policy and gradually expand your whitelist based on legitimate business needs. Document everything, test thoroughly, and maintain regular communication with your users.

Frequently Asked Questions

Q: Will this affect Firefox profiles already configured?
A: Group Policy settings override user preferences. Existing bookmarks and history remain intact, but site access follows your whitelist.

Q: Can users bypass this using incognito/private mode?
A: No. Group Policy applies to all Firefox browsing modes.

Q: What happens if a whitelisted site loads content from blocked domains?
A: The site may function partially or not at all. You’ll need to whitelist required CDN and API domains.

Q: Can I temporarily grant access to blocked sites?
A: Yes, but it requires GPO modification. For temporary access, consider creating a separate OU with a more permissive policy and moving computers there temporarily.

Q: Does this work with Firefox ESR?
A: Yes, Firefox Extended Support Release works perfectly with these Group Policy configurations.