Looks like the cookie banner blocker, originally scheduled for Firefox 114, didn’t make it into today’s Firefox 115 either. Brave and DuckDuckGo already block cookie banners.
For Firefox, we need to rely on uBlock Origin. Unfortunately, there’s no uBlock Origin for Firefox on iOS.
As far as I can tell, you can set cookiebanners.service.mode and cookiebanners.service.mode.privateBrowsing to 1 to enable the feature as far back as 114. There may be fixes in future versions, so check there before reporting bugs.