v86 describes its emulated ATAPI CD-ROM as non-removable in the IDENTIFY
PACKET DEVICE data (ATAPI_CFG_REMOV clear).  The cd(4) driver only matches
removable devices, so the drive attaches as uk0 ("unknown") instead of cd0:

    uk0 at atapibus0 drive 0: <v86 ATAPI CD-ROM, 8086-8610, 1.00> cdrom fixed

and the files the browser page hands to the guest as a CD cannot be mounted
at all.  Every ATAPI CD-ROM is removable by definition, so trust the device
type over the (missing) removable bit.

--- a/sys/dev/scsipi/atapi_wdc.c
+++ b/sys/dev/scsipi/atapi_wdc.c
@@ -306,7 +306,14 @@
 			periph->periph_dbflags |= SCSIPI_DEBUG_FLAGS;
 #endif
 		periph->periph_type = ATAPI_CFG_TYPE(id->atap_config);
-		if (id->atap_config & ATAPI_CFG_REMOV)
+		/*
+		 * Some emulated drives (notably v86) leave the removable bit
+		 * clear; an ATAPI CD-ROM is always removable, and cd(4) only
+		 * matches removable devices, so without this the drive
+		 * attaches as uk(4) and cannot be mounted.
+		 */
+		if ((id->atap_config & ATAPI_CFG_REMOV) ||
+		    periph->periph_type == T_CDROM)
 			periph->periph_flags |= PERIPH_REMOVABLE;
 		if (periph->periph_type == T_SEQUENTIAL) {
 			s = splbio();
@@ -316,8 +323,9 @@
 
 		sa.sa_periph = periph;
 		sa.sa_inqbuf.type =  ATAPI_CFG_TYPE(id->atap_config);
-		sa.sa_inqbuf.removable = id->atap_config & ATAPI_CFG_REMOV ?
-		    T_REMOV : T_FIXED;
+		sa.sa_inqbuf.removable =
+		    ((id->atap_config & ATAPI_CFG_REMOV) ||
+		    sa.sa_inqbuf.type == T_CDROM) ? T_REMOV : T_FIXED;
 		strnvisx(model, sizeof(model), id->atap_model,
 		    sizeof(id->atap_model), VIS_TRIM|VIS_SAFE|VIS_OCTAL);
 		strnvisx(serial_number, sizeof(serial_number),