[GH-ISSUE #370] Firefox Developer Edition doesn't recognise Mkcert issuing authority

kerem commented

2026-02-25 22:32:56 +03:00

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Originally created by @aindriu80 on GitHub (Jun 7, 2021).
Original GitHub issue: https://github.com/FiloSottile/mkcert/issues/370

Hi,

I have been using Mkcert for a while now to provide HTTPS on a local machine (Ubuntu 21.04) and Firefox (89.0 (64-bit)) it was working ok but I started using Firefox Developer Edition (90.0b3 (64-bit)) and I get the error below (Mkcert is not a recognized authority).

Someone could be trying to impersonate the site and you should not continue. Websites prove their identity via certificates. Firefox Developer Edition does not trust localhost:3000 because its certificate issuer is unknown, the certificate is self-signed, or the server is not sending the correct intermediate certificates. Error code: SEC_ERROR_UNKNOWN_ISSUER

Is there some way around this? It works perfectly in regular Firefox but not in the developer edition for some reason.

Originally created by @aindriu80 on GitHub (Jun 7, 2021). Original GitHub issue: https://github.com/FiloSottile/mkcert/issues/370 Hi, I have been using Mkcert for a while now to provide HTTPS on a local machine (Ubuntu 21.04) and Firefox (89.0 (64-bit)) it was working ok but I started using Firefox Developer Edition (90.0b3 (64-bit)) and I get the error below (Mkcert is not a recognized authority). ![2021-06-07_15-20](https://user-images.githubusercontent.com/8885837/121033673-4c15e780-c7a4-11eb-9fe4-035ec2a91203.png) > Someone could be trying to impersonate the site and you should not continue. Websites prove their identity via certificates. Firefox Developer Edition does not trust localhost:3000 because its certificate issuer is unknown, the certificate is self-signed, or the server is not sending the correct intermediate certificates. **Error code: SEC_ERROR_UNKNOWN_ISSUER** Is there some way around this? It works perfectly in regular Firefox but not in the developer edition for some reason.

kerem commented

2026-02-25 22:32:56 +03:00

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@ashleyconnor commented on GitHub (Jun 7, 2021):

Not a Linux user but have you tried installing the Root CA manually in the Firefox settings?

Instructions should be similar to here: https://ddev.readthedocs.io/en/stable/#windows-and-firefox-mkcert-install-additional-instructions

@ashleyconnor commented on GitHub (Jun 7, 2021): Not a Linux user but have you tried installing the Root CA manually in the Firefox settings? Instructions should be similar to here: https://ddev.readthedocs.io/en/stable/#windows-and-firefox-mkcert-install-additional-instructions

kerem commented

2026-02-25 22:32:56 +03:00

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@benjibee commented on GitHub (Feb 2, 2022):

I'm using Firefox v96.0.3 and getting this SEC_ERROR_UNKNOWN_ISSUER error myself. No such errors in Chrome or Safari. mkcert shows no error installing the cert in Firefox and manually installing the root CA says it's already installed. Any other people having this issue?

@benjibee commented on GitHub (Feb 2, 2022): I'm using Firefox v96.0.3 and getting this `SEC_ERROR_UNKNOWN_ISSUER` error myself. No such errors in Chrome or Safari. mkcert shows no error installing the cert in Firefox and manually installing the root CA says it's already installed. Any other people having this issue?

kerem commented

2026-02-25 22:32:56 +03:00

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@akositey commented on GitHub (Jul 22, 2022):

Had the same issue. I'm in Fedora 36 Workstation and it worked on Firefox and Chromium but newly installed Firefox Developer Edition (102.0) doesn't recognize CA.
In my case, running mkcert -install again and restarting Firefox Dev solved it.

@akositey commented on GitHub (Jul 22, 2022): Had the same issue. I'm in Fedora 36 Workstation and it worked on Firefox and Chromium but newly installed Firefox Developer Edition (102.0) doesn't recognize CA. In my case, running `mkcert -install` again and restarting Firefox Dev solved it.

kerem commented

2026-02-25 22:32:56 +03:00

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@DenisLanz commented on GitHub (Jul 25, 2022):

I had the same issue on macOS and Firefox Developer Edition, enabling the preference security.enterprise_roots.enabled to true solved this for me:

Enter “about:config” in the address bar and continue to the list of preferences.

Set the preference "security.enterprise_roots.enabled" to true.

Restart Firefox.

@DenisLanz commented on GitHub (Jul 25, 2022): I had the same issue on macOS and Firefox Developer Edition, enabling the preference `security.enterprise_roots.enabled ` to `true` solved this for me: > 1. Enter “about:config” in the address bar and continue to the list of preferences. > 2. Set the preference "security.enterprise_roots.enabled" to true. > 3. Restart Firefox.

kerem commented

2026-02-25 22:32:56 +03:00

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@Moongazer commented on GitHub (Sep 16, 2022):

Having the same issue in Ubuntu 22.04.01 LTS using DDEV: it works in Chromium but not in regular Firefox 104.0.2 (the security.enterprise_roots.enabled=true solution didn't work for me). First thought was, that the Snap package of Firefox might be the problem, because Snap makes often trouble with external files and folders. But strangely the Chromium Browser comes also as Snap package, so probably that's not the troublemaker here.

@Moongazer commented on GitHub (Sep 16, 2022): Having the same issue in Ubuntu 22.04.01 LTS using DDEV: it works in Chromium but not in regular Firefox 104.0.2 (the `security.enterprise_roots.enabled=true` solution didn't work for me). First thought was, that the Snap package of Firefox might be the problem, because Snap makes often trouble with external files and folders. But strangely the Chromium Browser comes also as Snap package, so probably that's not the troublemaker here.

kerem commented

2026-02-25 22:32:56 +03:00

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@nikolay-jobiqo commented on GitHub (Sep 19, 2022):

Having same issue as @Moongazer. Please let me know if you will fix this issue. Ubuntu 22.04.1 ddev, Firerfox 104.0.2 (64-bit)

@nikolay-jobiqo commented on GitHub (Sep 19, 2022): Having same issue as @Moongazer. Please let me know if you will fix this issue. Ubuntu 22.04.1 ddev, Firerfox 104.0.2 (64-bit)

kerem commented

2026-02-25 22:32:56 +03:00

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@Gernott commented on GitHub (Oct 17, 2022):

Same problem here since upgrading to Ubuntu 22.04.
Solution:

Open the Firefox Preferences
Enter certificates into the search box on the top
Click View Certificates...
Select the tab Authorities
Click to Import...
Go to the folder where your root certificate authority was stored (~/.local/share/mkcert)
Select the file rootCA.pem
Click to Open

@Gernott commented on GitHub (Oct 17, 2022): Same problem here since upgrading to Ubuntu 22.04. Solution: - Open the Firefox Preferences - Enter certificates into the search box on the top - Click View Certificates... - Select the tab Authorities - Click to Import... - Go to the folder where your root certificate authority was stored (~/.local/share/mkcert) - Select the file rootCA.pem - Click to Open

kerem commented

2026-02-25 22:32:56 +03:00

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@nikolay-jobiqo commented on GitHub (Oct 17, 2022):

@Gernott thanks a lot, works for me.

@nikolay-jobiqo commented on GitHub (Oct 17, 2022): @Gernott thanks a lot, works for me.

kerem commented

2026-02-25 22:32:56 +03:00

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@Moongazer commented on GitHub (Oct 17, 2022):

@Gernott This manual way works for me as well, thank you!

Edit:
MacOS users will find the file in ~/Library/Application Support/mkcert

@Moongazer commented on GitHub (Oct 17, 2022): @Gernott This manual way works for me as well, thank you! **Edit:** MacOS users will find the file in `~/Library/Application Support/mkcert`

kerem commented

2026-02-25 22:32:56 +03:00

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@quentinDupont commented on GitHub (Oct 28, 2022):

Hello !
Can't do "Go to the folder where your root certificate authority was stored (~/.local/share/mkcert)" because my share/mkcert is in /root/ folder and Firefox can't access it. Is it normal to have it in /root folder ?

@quentinDupont commented on GitHub (Oct 28, 2022): Hello ! Can't do "Go to the folder where your root certificate authority was stored (~/.local/share/mkcert)" because my share/mkcert is in /root/ folder and Firefox can't access it. Is it normal to have it in /root folder ?

kerem commented

2026-02-25 22:32:56 +03:00

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@meshuamam commented on GitHub (Feb 17, 2023):

@quentinDupont run mkcert -install without sudo

@meshuamam commented on GitHub (Feb 17, 2023): @quentinDupont run `mkcert -install` without `sudo`

kerem commented

2026-02-25 22:32:56 +03:00

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@meshuamam commented on GitHub (Feb 17, 2023):

Same problem here since upgrading to Ubuntu 22.04. Solution:

Open the Firefox Preferences

Enter certificates into the search box on the top

Click View Certificates...

Select the tab Authorities

Click to Import...

Go to the folder where your root certificate authority was stored (~/.local/share/mkcert)

Select the file rootCA.pem

Click to Open

Is it possible to do this via shell script?

@meshuamam commented on GitHub (Feb 17, 2023): > Same problem here since upgrading to Ubuntu 22.04. Solution: > > * Open the Firefox Preferences > * Enter certificates into the search box on the top > * Click View Certificates... > * Select the tab Authorities > * Click to Import... > * Go to the folder where your root certificate authority was stored (~/.local/share/mkcert) > * Select the file rootCA.pem > * Click to Open Is it possible to do this via shell script?

kerem commented

2026-02-25 22:32:56 +03:00

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@owzim commented on GitHub (Mar 1, 2023):

@meshuamam

The install script scripts/install_ddev.sh does it with the regular FF, so maybe look there, how it's done.

@owzim commented on GitHub (Mar 1, 2023): @meshuamam The install script `scripts/install_ddev.sh` does it with the regular FF, so maybe look there, how it's done.

kerem commented

2026-02-25 22:32:56 +03:00

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@shdblowers commented on GitHub (Mar 27, 2023):

Same problem here since upgrading to Ubuntu 22.04. Solution:

* Open the Firefox Preferences

* Enter certificates into the search box on the top

* Click View Certificates...

* Select the tab Authorities

* Click to Import...

* Go to the folder where your root certificate authority was stored (~/.local/share/mkcert)

* Select the file rootCA.pem

* Click to Open

This worked for me, can it be added to the install instructions for firefox?

@shdblowers commented on GitHub (Mar 27, 2023): > Same problem here since upgrading to Ubuntu 22.04. Solution: > > * Open the Firefox Preferences > > * Enter certificates into the search box on the top > > * Click View Certificates... > > * Select the tab Authorities > > * Click to Import... > > * Go to the folder where your root certificate authority was stored (~/.local/share/mkcert) > > * Select the file rootCA.pem > > * Click to Open This worked for me, can it be added to the install instructions for firefox?

kerem commented

2026-02-25 22:32:56 +03:00

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@sanjayojha commented on GitHub (Apr 25, 2023):

@Gernott thanks. This worked for also, However I have to click "Edit Trust" and then check mark the "This certificate can identify websites."

@sanjayojha commented on GitHub (Apr 25, 2023): @Gernott thanks. This worked for also, However I have to click "Edit Trust" and then check mark the "This certificate can identify websites."

kerem commented

2026-02-25 22:32:56 +03:00

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@arnofly commented on GitHub (Sep 9, 2023):

I had the same issue on macOS and Firefox Developer Edition, enabling the preference security.enterprise_roots.enabled to true solved this for me:

Enter “about:config” in the address bar and continue to the list of preferences.

Set the preference "security.enterprise_roots.enabled" to true.

Restart Firefox.

~~For a local development environment using the specific Firefox version, I found DenisLanz's solution to be effective."~~

DenisLanz's solution is totally secure, thank!
https://support.mozilla.org/en-US/kb/setting-certificate-authorities-firefox

@arnofly commented on GitHub (Sep 9, 2023): > I had the same issue on macOS and Firefox Developer Edition, enabling the preference `security.enterprise_roots.enabled ` to `true` solved this for me: > > > 1. Enter “about:config” in the address bar and continue to the list of preferences. > > 2. Set the preference "security.enterprise_roots.enabled" to true. > > 3. Restart Firefox. ~~For a local development environment using the specific Firefox version, I found DenisLanz's solution to be effective."~~ DenisLanz's solution is totally secure, thank! [https://support.mozilla.org/en-US/kb/setting-certificate-authorities-firefox](url)

kerem commented

2026-02-25 22:32:56 +03:00

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@gitressa commented on GitHub (Oct 10, 2023):

I just ran into this with Firefox installed via Flatpak, maybe the reason? @Gernott's tip worked perfectly, thanks!

@gitressa commented on GitHub (Oct 10, 2023): I just ran into this with Firefox installed via Flatpak, maybe the reason? @Gernott's [tip](https://github.com/FiloSottile/mkcert/issues/370#issuecomment-1280377305) worked perfectly, thanks!

kerem commented

2026-02-25 22:32:56 +03:00

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@ajpgtech commented on GitHub (Dec 20, 2023):

mkcert -install
The local CA is already installed in the system trust store! 👍
Warning: "certutil" is not available, so the CA can't be automatically installed in Firefox and/or Chrome/Chromium! ⚠️
Install "certutil" with "apt install libnss3-tools" and re-run "mkcert -install" 👈

Therefore

apt install libnss3-tools
mkcert -install

@ajpgtech commented on GitHub (Dec 20, 2023): ``` mkcert -install The local CA is already installed in the system trust store! 👍 Warning: "certutil" is not available, so the CA can't be automatically installed in Firefox and/or Chrome/Chromium! ⚠️ Install "certutil" with "apt install libnss3-tools" and re-run "mkcert -install" 👈 ``` Therefore ``` apt install libnss3-tools mkcert -install ```

kerem commented

2026-02-25 22:32:57 +03:00

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@Servermonkk commented on GitHub (Aug 20, 2024):

@Gernott Thanks it worked perfectly!

@Servermonkk commented on GitHub (Aug 20, 2024): @Gernott Thanks it worked perfectly!

kerem commented

2026-02-25 22:32:57 +03:00

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@sdanielch commented on GitHub (Aug 14, 2025):

Same problem here since upgrading to Ubuntu 22.04. Solution:

* Open the Firefox Preferences

* Enter certificates into the search box on the top

* Click View Certificates...

* Select the tab Authorities

* Click to Import...

* Go to the folder where your root certificate authority was stored (~/.local/share/mkcert)

* Select the file rootCA.pem

* Click to Open

Perfect! Its worked! Thanks (FLATPAK VERSION)

@sdanielch commented on GitHub (Aug 14, 2025): > Same problem here since upgrading to Ubuntu 22.04. Solution: > > * Open the Firefox Preferences > > * Enter certificates into the search box on the top > > * Click View Certificates... > > * Select the tab Authorities > > * Click to Import... > > * Go to the folder where your root certificate authority was stored (~/.local/share/mkcert) > > * Select the file rootCA.pem > > * Click to Open Perfect! Its worked! Thanks (FLATPAK VERSION)

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[GH-ISSUE #370] Firefox Developer Edition doesn't recognise Mkcert issuing authority #241