Windows XP and Android 2.x comes to mind. Non-HTTP protocols (IMAP, SMTP, XMPP, SIP etc) may also struggle with SNI.
But the biggest problem here is wildcarded subdomains, since LE doesn't let you get more than 5 certificates per domain.
But the biggest problem here is wildcarded subdomains, since LE doesn't let you get more than 5 certificates per domain.
Also I think with Firefox on Windows XP it should work.