Have you thought about adding paid features or anything like that? I made a service that makes it really easy — https://extensionpay.com It's open source and works across all browsers.
I hear you that you want to keep your project free, but I'd also like to point out that it doesn't matter if your project is open-source or not to use ExtensionPay!
For example, the extension NotionBoost is open source and also uses ExtensionPay for paid features: https://gourav.io/notion-boost
[0] https://news.ycombinator.com/item?id=27327892
[1] https://github.com/extesy/hoverzoom/discussions/670
2 months to this, impressive