<s>
XPInstall	B-Application
(	O
Cross-Platform	O
Install	O
)	O
is	O
a	O
technology	O
used	O
by	O
the	O
Mozilla	B-Language
Application	I-Language
Suite	I-Language
,	O
SeaMonkey	B-Language
,	O
Mozilla	B-Application
Firefox	I-Application
,	O
Mozilla	B-Application
Thunderbird	I-Application
and	O
other	O
XUL-based	O
applications	O
for	O
installing	O
Mozilla	B-Operating_System
extensions	I-Operating_System
that	O
add	O
functionality	O
to	O
the	O
main	O
application	O
.	O
</s>
<s>
A	O
XPI	B-Application
(	O
pronounced	O
"	O
zippy	O
"	O
and	O
derived	O
from	O
XPInstall	B-Application
)	O
installer	O
module	O
is	O
a	O
ZIP	B-General_Concept
file	I-General_Concept
that	O
contains	O
an	O
install	O
script	O
or	O
a	O
manifest	O
at	O
the	O
root	O
of	O
the	O
file	O
,	O
and	O
a	O
number	O
of	O
data	O
files	O
.	O
</s>
<s>
In	O
Mozilla	O
,	O
Firefox	B-Application
before	O
0.7	O
,	O
and	O
before	O
0.5	O
,	O
the	O
package	O
contained	O
a	O
JavaScript	B-Language
install	O
script	O
(	O
install.js	O
)	O
with	O
some	O
directives	O
for	O
actions	O
to	O
take	O
during	O
an	O
install	O
,	O
including	O
adding	O
files	O
and	O
directories	O
,	O
removing	O
old	O
or	O
obsolete	O
files	O
and	O
directories	O
,	O
executing	O
command	O
line	O
tools	O
,	O
etc	O
.	O
</s>
<s>
In	O
middle-old	O
Firefox	B-Application
and	O
Thunderbird	B-Application
versions	O
,	O
the	O
install	O
script	O
has	O
been	O
replaced	O
by	O
a	O
chrome	B-Application
manifest	O
and	O
a	O
RDF	O
file	O
(	O
install.rdf	O
)	O
.	O
</s>
<s>
Since	O
Firefox	B-Application
version	O
45	O
,	O
the	O
only	O
mandatory	O
file	O
is	O
manifest.json	O
.	O
</s>
<s>
Since	O
Firefox	B-Application
1.0	O
,	O
XPIs	B-Application
from	O
sites	O
other	O
than	O
Mozilla	O
Add-ons	B-Operating_System
are	O
blocked	O
by	O
default	O
.	O
</s>
<s>
While	O
it	O
is	O
possible	O
to	O
put	O
a	O
site	O
into	O
the	O
whitelist	O
that	O
limits	O
sites	O
which	O
can	O
install	O
XPIs	B-Application
,	O
malicious	O
sites	O
cannot	O
install	O
extensions	O
in	O
the	O
background	O
(	O
without	O
human	O
intervention	O
)	O
.	O
</s>
