Generating GUIDs

GUIDs are used in Mozilla programming for identifying several types of entities, including XPCOM Interfaces (this type of GUIDs is callled IID), components (CID), and legacy add-ons—like extensions and themes—that were created prior to Firefox 1.5. Add-ons can (and should) be identified with IDs of the form extensionname@organization.tld since Firefox 1.5.

Warning: If you just want an ID for your add-on, generating a GUID is almost definitely not what you want to do. Using the extensionname@organization.tld form is approximately one thousand times easier for everyone involved. Don't have a domain name? Do you have a blog on a subdomain? Use that. If all else fails, using extensionname@yourusername.addons.mozilla.org should be fine; no one will care. Remember, these are identifiers, not e-mail addresses, and they're never resolved.

Canonical form

The common form of a GUID is xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx, where each x stands for a hexadecimal digit. There are a number of tools that can be used to generate a GUID in the canonical form.

Note: If you do choose to use an email-style ID for your add-on, you probably don't want it to be a real email address, since it might attract spam.

Online tools

Generate GUID Online
UUID (GUID) Generator on the WEB
UUID Generator for Mozilla Code (both IDL and C++.h forms)
You can get a GUID from one of the bots (such as botbot, firebot) on #firefox IRC channel by /msging "uuid" to them.

Windows

Windows users can use the GuidGen tool from Microsoft to obtain a GUID. (This tool is also part of MS Visual C++)

Linux

Use /usr/bin/uuidgen. This can be found in package uuid-runtime (Debian).

Mac OS X

Use /usr/bin/uuidgen.

Perl

jkeiser's Mozilla tools include a UUID generator with output format of both C++ and IDL style.
sfink's update-uuids will change the uuid for a given interface and all of its descendants, updating all *.idl files within a directory tree.

nsIUUIDGenerator

A UUID can be generated from privileged Mozilla code using nsIUUIDGenerator. See the linked page for details.

COM/XPCOM format

When #define-ing IIDs and CIDs in Mozilla C++ code, you generally use the following format:

// xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxx
#define NS_...ID \
{ 0xXXXXXXXX, 0xXXXX, 0xXXXX, \
  { 0xXX, 0xXX, 0xXX, 0xXX, 0xXX, 0xXX, 0xXX, 0xXX } }

You can generate code in this format using one of the following tools.

Online tools

http://mozilla.pettay.fi/cgi-bin/mozuuid.pl

guidgen

guidgen.exe, part of Microsoft Visual Studio, can generate UUIDs in this format.

bash

You can put the following into your .bashrc file:

uuidgen-c++()
{
    local UUID=$(uuidgen)
    echo "// $UUID"
    echo "#define NS__IID \\"
    echo "{ 0x${UUID:0:8}, 0x${UUID:9:4}, 0x${UUID:14:4}, \\"
    echo -n "  { 0x${UUID:19:2}, 0x${UUID:21:2}, 0x${UUID:24:2}, "
    echo -n "0x${UUID:26:2}, 0x${UUID:28:2}, 0x${UUID:30:2}, "
    echo "0x${UUID:32:2}, 0x${UUID:34:2} } }"
}

Perl

#!/usr/bin/perl
$uuid = `uuidgen`;
chomp $uuid;
print $uuid, "\n";
@parts = ($uuid =~ /^(.{8})-(.{4})-(.{4})-(..)(..)-(..)(..)(..)(..)(..)(..)$/);
print "{ 0x$parts[0], 0x$parts[1], 0x$parts[2], \\", "\n", " { ";
for (3 .. 9) {
  print "0x$parts[$_], ";
}
print "0x$parts[10] } }", "\n";