How to Fix the “ssl_error_no_cypher_overlap” Error on Mozilla Firefox

The “ssl_error_no_cypher_overlap” error on Mozilla Firefox means that your browser and the server to which you’re trying to connect cannot agree upon something called a “cipher suite”. This particular error code is specific to Mozilla Firefox browser, even though other major browsers like Google Chrome have their own error messages to indicate the same problem.

Let’s look at what you can do to fix the ssl_error_no_cypher_overlap error and we’ll also talk about what a cipher suite actually is. If you’re using a 3rd party inverse-proxy site like Cloudflare for your website, I’ll also show you how to check the cipher suites, making it easy to obtain debugging info.

• Steps to Fix the “ssl_error_no_cypher_overlap” Error Code
  • #1. Update to the Latest Version of Firefox
  • #2. Check if You Can Access the Site on Another Browser
  • #3. Reset Any Modified TLS Settings in Firefox
  • #4. Reduce the TLS Fallback Limit Version
  • #5. Allow “Dangerous and Deceptive Content” on Firefox
• How to Check which Cipher Suite your Server Supports
• How to Check the List of Ciphers on The Mozilla Firefox Browser

Steps to Fix the “ssl_error_no_cypher_overlap” Error Code

Here are the steps you need to take to fix the error code ssl_error_no_cypher_overlap starting with the simplest solution, with each subsequent solution a bit more complex.

#1. Update to the Latest Version of Firefox

This should be your first attempt to solve the error code “ssl_error_no_cypher_overlap”. I know it sounds lame to just “update FireFox” – like the tech person on the call telling you to restart your device – but it’s possible that there is a new version of the available cipher suites or some new standard is enforced that makes certain websites accessible. There are other benefits to avoiding using an outdated version of Firefox anyway so it’s always good to get the latest version.

To update your Mozilla Firefox browser, go to the Firefox settings, and in the “General” tab, scroll down till you see the section labeled “Firefox Update”, and click “Check for updates” as shown here:

This is the easiest way to update Firefox and will ensure you are getting the latest version from the official Firefox website. After you update Firefox, clear your cookies, refresh your browser, and try again. If it doesn’t work, head to step 2.

#2. Check if You Can Access the Site on Another Browser

The next step is to see whether the problem is on your end or the website you’re trying to access. Accessing the site on another browser is the easiest way to do this. Ideally, try and access it on another device entirely, like a smart phone. Even better if you can disable the Wi-Fi on your smartphone and use the network connection to ensure a completely separate device and network connection.

If you get the same or a similar error, then it means that the problem is not isolated to your browser but is an issue with the server itself. If you’re not the website owner, then you can do nothing other than send a message to the owner and inform them of the problem. But even then, you might be able to work around the issue by implementing some other fixes below.

#3. Reset Any Modified TLS Settings in Firefox

The Firefox browser can throw the error ssl_error_no_cypher_overlap if you’ve changed some of the TLS settings or some extension has messed with the SSL settings. The first thing to try is to reset any modified TLS values in the Firefox configuration screen.

To access these settings, open the Firefox browser and type “about:config” in the URL bar. You’ll come to a screen with a scary warning informing you that you’re “voiding your warranty” or something like that, followed by a large list of settings. In the search box at the top of the screen, type “TLS” to filter the results. Normally, all these entries should be in regular font, but if any one of them is in bold, it means that something or someone has changed it.

Another easy option is to check the box on top that says “Show only modified preferences”, and this will bring up a list of options that have changed from the defaults, as shown here (in my screenshot, I haven’t modified anything):

If you see any entries here, right-click on each one and click “Reset” to set them back to their original values. Now reload your Firefox browser, clear your cookies, and refresh the page hard. With some luck, the ssl_error_no_cypher_overlap error code would have vanished!

#4. Reduce the TLS Fallback Limit Version

So far, we’ve only looked at solutions that try and fix potential problems and configurations that may be causing the ssl_error_no_cypher_overlap error code. However, if you’re desperate to access the site at any price, there are a few things you can do that could allow you to access it at the expense of reduced security.

It’s important to note that the following steps will impact your browser’s security, and you should reverse them as soon as you can so that you can browse other websites without worrying about malicious sites or your sensitive information being stolen.

As before, go to “about:config” in your Firefox browser, and after agreeing to the warning, type “security.tls.version” into the search box as shown here:

In the following list, change the following settings;

1. security.tls.version.fallback-limit => set this to “0”
2. security.tls.version.min => set this to “0”

These settings are meant to put a floor on the cipher suite versions that the browser and server negotiate. Since getting an ssl_error_no_cypher_overlap error code means that the Firefox browser and server can’t agree upon a cipher suite, the above change increases the range of values upon which they can agree. In the worst-case scenario, they will settle on a protocol that isn’t safe but a low enough version that they both support it.

As mentioned above, this will lower the security of your Firefox browser. You should use this only to access the specific website you want and then immediately change the about:config setting back to what it was.

#5. Allow “Dangerous and Deceptive Content” on Firefox

This step is potentially even more dangerous that the previous one since it requires modifying Firefox’s behavior to allow through sites that it would normally block. As before, ensure that you revert this setting as soon as possible.

Go to the Firefox settings page, and select “Privacy & Security” on the left-hand side as shown here:

As shown above, uncheck the first box under the heading “Deceptive Content and Dangerous Software Protection”. Unchecking the main box will also disable the two boxes underneath.

This will remove the default settings of blocking dangerous and deceptive content in Mozilla Firefox.

After you do this, try to access the site you couldn’t, thanks to the “ssl_error_no_cypher_overlap” error. If your browser was blocking the site because it was unsafe, you might be able to see it now.

And not to belabor a point – change the setting back when you’re done with it! It’s never a good idea to bypass browser security protocols in general.

How to Check which Cipher Suite your Server Supports

If you’re trying to debug the “ssl_error_no_cypher_overlap” error code on Firefox, you should start by listing all the cipher suites the server currently offers. If you don’t have access to the server, you can do nothing about it. But if you do, then log in via SSH and type the following into the command line:

/usr/bin/openssl ciphers -v

You should see something like this:

This is a list of ciphers my website WP-Tweaks.com. As you can see, it’s quite a long list, which means there’s a lot to choose from when negotiating a suite with Firefox.

How to Check the List of Ciphers on The Mozilla Firefox Browser

If you want to check the list of cipher suites on Firefox, the process is a bit more complicated, as there’s no native way to do it. To start, you’ll need to clone this git repository and run this python command:

python server.py -p 4433

Then point your browser to https://localhost:4433/. You should see something like this:

Binding…
Connection from ('127.0.0.1', 64814)
Record Version: TLS1_0
Handshake Version: TLS1_2
Session ID Length: 0
Cipher Suites Length (bytes): 26
Cipher Suites:
0xc02b TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
0xc02f TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
0xcca9 TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256
0xcca8 TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256
0xc02c TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
0xc030 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
0xc00a TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
0xc009 TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
0xc013 TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
0xc014 TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
0x002f TLS_RSA_WITH_AES_128_CBC_SHA
0x0035 TLS_RSA_WITH_AES_256_CBC_SHA
0x000a TLS_RSA_WITH_3DES_EDE_CBC_SHA

These are the lists of possible ciphers. You can also visit https://browserleaks.com/ssl and check which ciphers Firefox is using currently as shown here:

Using this information, you could debug the error code “ssl_error_no_cypher_overlap” and try and figure out why the server and Firefox cannot agree on common ground.

I hope you find what you’re looking for and that this article was helpful. Browser errors can sometimes be a lot more complex than what they first appear like. Hopefully by avoiding older FireFox versions and updating Firefox regularly, you can prevent the error code ssl_error_no_cypher_overlap from popping up in most cases.