Mozilla got back to me on my extension today - it was rejected and had the following helpful workaround:
We experienced an issue that significantly delayed the review of add-ons using the proxy API permission. This issue has been resolved for add-ons targeting Firefox 91.1 and above.
We apologize for the long delays you may have experienced in the queue. As we are now able to more quickly review add-on versions targeting Firefox 91.1 and above, please update the browser_specifics_settings key of your extension’s manifest.json with the following and submit a new version:
"browser_specific_settings": {
"gecko": {
"strict_min_version": "91.1.0"
}
}
See browser_specific_settings - Mozilla | MDN for more information about this key.
Thank you for developing extensions for Firefox!
After adding this top-level key, I resubmitted and now it’s live! 