If anyone else is having the same issue, I found the file at: https://github.com/pfn/keepasshttp/blob/master/KeePassHttp.plgx - it would be nice if the instructions above could update their link!

Also it does not specify *where* I'm looking for "go to Tools > Plugins" but it looks like it's in KeePass itself. Loading the file didn't make it appear, but restarting the program did.

I'm attempting to update since it stopped working when I updated to KeePass 2.50 but https://passifox.appspot.com/KeePassHttp.plgx gets a 500 server error.
Any idea what's up?