The basic problem stems from a too-liberal use of the  (?:\b|_) assertion.

The  $parse1 string begins with a  / (forward slash) character. This is not a \w character. The  (?:\b|_) assertions in  (?:\b|_)$parse1(?:\b|_) require that  $parse1 be preceded by a \w character or a  _ (underscore) (note that  _ is a member of the \w class), and followed by a non-\w character or a  _ (underscore).

What the OPed regex will match depends on the string it is matching against. I would advise giving us examples of typical strings. Below are some examples of mine that show various matches/non-matches:

c:\@Work\Perl>perl -wMstrict -le
"print qq{perl version: $] \n};
 ;;
 my $parse1 = '/newsearch/detail/96603';
 my $parse2 = '';
 ;;
 for (
   qq{xxx \n/newsearch/detail/96603\n xxx},
   qq{xxx \n/newsearch/detail/96603x\n xxx},
   qq{xxx \nx/newsearch/detail/96603x\n xxx},
   qq{xxx \nx/newsearch/detail/96603\n xxx},
   qq{bla vla/newsearch/detail/96603 x},
   ) {
   print qq{<<$_>>};
   print qq{MATCH '$&'} if
     /^.*?(?:\b|_)$parse1(?:\b|_).*?(?:\b|_)$parse2(?:\b|_).*?$/m;
   print '';
   }
"
perl version: 5.008009

<<xxx
/newsearch/detail/96603
 xxx>>

<<xxx
/newsearch/detail/96603x
 xxx>>

<<xxx
x/newsearch/detail/96603x
 xxx>>

<<xxx
x/newsearch/detail/96603
 xxx>>
MATCH 'x/newsearch/detail/96603'

<<bla vla/newsearch/detail/96603 x>>
MATCH 'bla vla/newsearch/detail/96603 x'
[download]

Update: Because you give no examples of the typical strings you're matching against, I cannot understand the implications of the  ^.*? and  .*?$ and  .*?(?:\b|_)$parse2(?:\b|_) portions of the OPed regex (which I suspect may be superfluous), or why you are matching in  /m "multi-line" mode.