Firefox seems to be respecting CORS, where Chrome does not, which is interesting. As a result the site doesn't work on Firefox. (at least for me).

   Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://www.reddit.com/search.json?q=(site:v.redd.it%20OR%20site:youtube.com%20OR%20site:vimeo.com%20OR%20site:youtu.be%20OR%20site:twitch.tv%20OR%20site:gfycat.com%20OR%20site:streamable.com%20OR%20site:tiktok.com%20OR%20site:livestream.com%20OR%20site:dailymotion.com%20OR%20site:rumble.com%20OR%20site:liveleak.com%20OR%20site:gifs.com%20OR%20site:giphy.com%20OR%20site:redgifs.com%20OR%20site:bandcamp.com)%20NOT%20url:feature=share%20NOT%20url:vm.tiktok.com%20NOT%20url:music.youtube.com&t=hour&sort=comments&sr_detail=on&limit=12&nsfw=no&include_over_18=no. (Reason: CORS request did not succeed).

Edit: As noted below, if you are running Firefox in Strict privacy protection, it blocks the XHR requests. Whitelisting this site will allow it to work.