Wether you have chosen Microsoft Advertising (formerly Xandr) as your adserver and/or using it as a prebid bidder or your main programmatic ssp, first-id can be leveraged in many ways to cover your activations without any browser limitations, across all your users.
How can I do that ?
Please refer to this documentation on how to use the first-id in your Microsoft Advertising tools (Monetize / Curate ).