Blocked by Ublock: SameSite atribute and Cross-Origin Request Blocked

When inspecting in Firefox after a full and working setup of serverside GA4 and GTM according your guides I test it with Ublock on in Firefox and I get the following erros in the Network panel:

  1. Some cookies are missing the recommended “SameSite“ attribute (the listed cookies are all ga cookies)
  2. Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at followed by an endpoint with my custom gtm.domain subdomain and folder /g/collect? and a lot of parameters.

I’m realy a newbee into this and I’m not realy sure where to look next.

Kind regards,


For item 1 - unless you changes something, that’s a default behaviour of GA4, so I wouldn’t dwell on it much

For item 2 - need a URL where we can check this, you can DM me if you don’t want to expose it

Thanks for the reply Dan! So the issue is on in Firefox with the extention (addblocker) UBlock Origin ON. Without the add blocker I only get the: “Some cookies are misusing the recommended “SameSite“ attribute” error.

@Sjoerd I don’t think that’s CORS related as your original message suggests, it looks like UBlock is recognising the /collect pattern (GA4 hits) and blocks based on that, when I try to send the same hit with a different pattern - everything goes through.

No remedy for this presently (this GA4 specifically, you can see that gtm is still loaded) although we may yet come up with something

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