If you right-click (or Ctrl+click) the blue button and click Save Link As, can you get a more informative error message? You also could check the Browser Console (Command+Option+J) to see whether there is an error with the CDN redirect or some kind of block.

Note that you posted with a Nightly build, does this also happen with the current release?

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works, you can transfer files from a previously used profile to the new profile, but be careful not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

If you right-click (or Ctrl+click) the blue button and click Save Link As, can you get a more informative error message? You also could check the Browser Console (Command+Option+J) to see whether there is an error with the CDN redirect or some kind of block.

1. "Save Link As" downloads the extension as an xpi file to my Downloads folder, so that seems ok?
2. On the dev tools network tab, I can only see GET requests to googleanalytics when I click the blue button

Note that you posted with a Nightly build, does this also happen with the current release? You can create a new profile as a quick test to see if your current profile is causing the problem. See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works, you can transfer files from a previously used profile to the new profile, but be careful not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

It happens on a brand new profile. I've updated Nightly a couple of times in the past 2 days already.

jscher2000 - Support Volunteer said

If you right-click (or Ctrl+click) the blue button and click Save Link As, can you get a more informative error message? You also could check the Browser Console (Command+Option+J) to see whether there is an error with the CDN redirect or some kind of block.

1. "Save Link As" downloads the extension as an xpi file to my Downloads folder, so that seems ok?
2. On the dev tools network tab, I can only see GET requests to googleanalytics when I click the blue button

Thank you for testing. #1 sounds good. For #2, the retrieval probably won't appear in a given tab's Network list, you would need to enable network logging in the Browser Console (gear icon at the right end of that window's filter bar).

It's a work laptop

Do you see any active policies if you visit about:policies in the address bar?

Are you able to install the downloaded xpi manually?

Hi both, thanks for your help so far. I realised that our company is using Netskope to control traffic on our laptops and addons.mozilla.org (or something similar) wasn't allowlisted. I asked for it to be added but the response was that Firefox has some security issues (I'm not sure what exactly) and it's not a supported browser for us, so unfortunately I'm going to have to use Google Chrome.

I also checked my personal PC and addons can be downloaded there without any issues. It also doesn't have the Mozilla certificate I mentioned in the original post. At this point I'm confident the issue is due to the company's network configuration.

Well, that's frustrating!

If they do not block or prohibit extensions in Firefox but merely block the Add-ons website, then you can always download the extension elsewhere to a removable USB device and install the extension locally.

Did you try manually installing the extension xpi file like I mentioned?