<s>
Cross	B-Application
Platform	I-Application
Component	I-Application
Object	I-Application
Model	I-Application
(	O
XPCOM	B-Application
)	O
is	O
a	O
cross-platform	B-Operating_System
component	B-Architecture
model	I-Architecture
from	O
Mozilla	B-Operating_System
.	O
</s>
<s>
It	O
is	O
similar	O
to	O
Microsoft	B-Application
Component	I-Application
Object	I-Application
Model	I-Application
(	O
COM	O
)	O
and	O
Common	B-Architecture
Object	I-Architecture
Request	I-Architecture
Broker	I-Architecture
Architecture	I-Architecture
(	O
CORBA	B-Architecture
)	O
.	O
</s>
<s>
It	O
features	O
multiple	O
language	B-Application
bindings	I-Application
and	O
interface	B-General_Concept
description	I-General_Concept
language	I-General_Concept
(	O
IDL	O
)	O
descriptions	O
;	O
thus	O
programmers	O
can	O
plug	O
their	O
custom	O
functions	O
into	O
the	O
framework	O
and	O
connect	O
it	O
with	O
other	O
components	O
.	O
</s>
<s>
The	O
most	O
prominent	O
usage	O
of	O
XPCOM	B-Application
is	O
within	O
the	O
Firefox	B-Application
web	I-Application
browser	I-Application
.	O
</s>
<s>
Many	O
of	O
its	O
internal	O
components	O
interact	O
via	O
XPCOM	B-Application
interfaces	O
.	O
</s>
<s>
Furthermore	O
,	O
Firefox	B-Application
used	O
to	O
allow	O
add-ons	B-Operating_System
extensive	O
XPCOM	B-Application
access	O
,	O
but	O
this	O
was	O
removed	O
in	O
2017	O
and	O
replaced	O
with	O
the	O
less-permissive	O
WebExtensions	B-Operating_System
API	O
.	O
</s>
<s>
(	O
Three	O
forks	B-Application
of	O
Firefox	B-Application
still	O
support	O
the	O
legacy	O
add-on	B-Operating_System
capability	O
:	O
Pale	B-Protocol
Moon	I-Protocol
,	O
Basilisk	O
,	O
Waterfox	B-Language
.	O
)	O
</s>
<s>
XPCOM	B-Application
is	O
one	O
of	O
the	O
main	O
things	O
making	O
the	O
Mozilla	B-Operating_System
application	O
environment	O
an	O
actual	O
framework	O
.	O
</s>
<s>
It	O
is	O
a	O
development	O
environment	O
that	O
provides	O
the	O
following	O
features	O
for	O
the	O
cross-platform	B-Operating_System
software	I-Operating_System
developer	O
:	O
</s>
<s>
This	O
component	B-Application
object	I-Application
model	I-Application
makes	O
virtually	O
all	O
of	O
the	O
functionality	O
of	O
Gecko	B-Language
available	O
as	O
a	O
series	O
of	O
components	O
,	O
or	O
reusable	O
cross-platform	B-Operating_System
libraries	B-Library
,	O
that	O
can	O
be	O
accessed	O
from	O
the	O
web	B-Application
browser	I-Application
or	O
scripted	O
from	O
any	O
Mozilla	B-Operating_System
application	O
.	O
</s>
<s>
Applications	O
that	O
must	O
access	O
the	O
various	O
Mozilla	B-Operating_System
XPCOM	B-Application
libraries	B-Library
(	O
networking	B-Architecture
,	O
security	O
,	O
DOM	B-General_Concept
,	O
etc	O
.	O
)	O
</s>
<s>
use	O
a	O
special	O
layer	O
of	O
XPCOM	B-Application
called	O
XPConnect	O
,	O
which	O
reflects	B-Language
the	O
library	O
interfaces	O
into	O
JavaScript	B-Language
,	O
or	O
other	O
languages	O
.	O
</s>
<s>
XPConnect	O
glues	O
the	O
front	O
end	O
to	O
the	O
C++	B-Language
,	O
C	B-Language
,	O
or	O
Rust	B-Application
programming	I-Application
language	I-Application
based	O
components	O
in	O
XPCOM	B-Application
,	O
and	O
it	O
can	O
be	O
extended	O
to	O
include	O
scripting	O
support	O
for	O
other	O
languages	O
:	O
PyXPCOM	O
already	O
offers	O
support	O
for	O
Python	B-Language
.	O
</s>
<s>
PerlConnect	O
and	O
plXPCOM	O
provide	O
support	O
for	O
Perl	B-Language
,	O
and	O
there	O
are	O
efforts	O
underway	O
to	O
add	O
Common	O
Language	O
Infrastructure	O
(	O
CLI	O
)	O
and	O
Ruby	B-Language
language	I-Language
support	O
for	O
XPConnect	O
.	O
</s>
<s>
For	O
developers	O
,	O
XPCOM	B-Application
allows	O
writing	O
components	O
in	O
C++	B-Language
,	O
C	B-Language
,	O
JavaScript	B-Language
,	O
Python	B-Language
,	O
or	O
other	O
languages	O
for	O
which	O
special	O
bindings	O
have	O
been	O
created	O
,	O
and	O
compile	O
and	O
run	O
those	O
components	O
on	O
dozens	O
of	O
different	O
platforms	O
,	O
including	O
these	O
and	O
others	O
where	O
Mozilla	B-Operating_System
is	O
supported	O
.	O
</s>
<s>
The	O
flexibility	O
to	O
reuse	O
the	O
XPCOM	B-Application
components	O
from	O
the	O
Gecko	B-Language
library	O
and	O
develop	O
new	O
components	O
that	O
run	O
on	O
different	O
platforms	O
facilitates	O
rapid	O
application	O
development	O
and	O
results	O
in	O
an	O
application	O
that	O
is	O
more	O
productive	O
and	O
easier	O
to	O
maintain	O
.	O
</s>
<s>
The	O
networking	B-Architecture
library	O
,	O
for	O
example	O
,	O
is	O
a	O
set	O
of	O
XPCOM	B-Application
components	O
that	O
can	O
be	O
accessed	O
and	O
used	O
by	O
any	O
Mozilla	B-Operating_System
application	O
.	O
</s>
<s>
File	O
I/O	O
,	O
security	O
,	O
password	O
management	O
,	O
and	O
profiles	O
are	O
also	O
separate	O
XPCOM	B-Application
components	O
that	O
programmers	O
can	O
use	O
in	O
their	O
own	O
application	O
development	O
.	O
</s>
<s>
XPCOM	B-Application
adds	O
a	O
lot	O
of	O
code	O
for	O
marshalling	B-Application
objects	O
,	O
and	O
in	O
the	O
Netscape	B-Protocol
era	O
XPCOM	B-Application
was	O
overused	O
for	O
internal	O
interfaces	O
where	O
it	O
was	O
n't	O
truly	O
necessary	O
,	O
resulting	O
in	O
software	O
bloat	O
.	O
</s>
<s>
This	O
was	O
a	O
key	O
reason	O
why	O
in	O
2001	O
Apple	O
forked	O
KHTML	B-Language
,	O
not	O
Gecko	B-Language
,	O
to	O
create	O
the	O
WebKit	B-Language
engine	B-Protocol
for	O
its	O
Safari	B-Application
browser	I-Application
.	O
</s>
<s>
Mozilla	B-Operating_System
has	O
since	O
cleaned	O
up	O
some	O
of	O
the	O
XPCOM	B-Application
bloat	O
.	O
</s>
<s>
By	O
2008	O
,	O
this	O
combined	O
with	O
other	O
efforts	O
resulted	O
in	O
big	O
performance	O
improvements	O
for	O
Gecko	B-Language
.	O
</s>
