Why structure this as a browser extension rather than pull-requests to the Lemmy web-ui? With Reddit, there was no path to contribute an improvement to the web-UI, so an extension was the only viable path to fix anything. By my sense is that the Lemmy core devs have been very receptive to external contributions, and have welcomed improvements from UX/UI experts.
Have you considered trying to adapt this to the Lemmy codebase and getting it merge so it’s available to everyone without a having to seek out and install a browser extension?