Why? The only things I had to customize again were the "theme", "show bookmark bar" and "ask where to download files everytime" settings. Everything else including history, passwords, saved bookmarks, installed extensions and chrome profiles were recognized.
Dunno what settings or configuration or connection quality you have set up but I don't have any problems watching youtube through firefox. You might want to start a thread to get to the root cause of the issue.
I think it can be work on 7 and 8.1 because Chrome's version 109.0.5414.129 which first only released for Windows Server 2012 and Windows Server 2012 R2 can work on 7 and 8.1. Just wait for the first version to be released and we will know.
The very latest Snapshot of Vivaldi works on W81 (for obvious reasons i use the 32bit version but the x64 works as well) I tested it on Server 2008R2 and it doesn't work,, BTW that OS is not fully updated (updated to around one year ago)