I don't think so. The discussions for this from 2010 refer to an annotated
#define from nsHttp.h in the Mozilla CVS tree:
// hard upper limit on the number of requests that can be pipelined
#define NS_HTTP_MAX_PIPELINED_REQUESTS 8
However, apparently, "For Gecko, XULRunner, and Firefox, CVS trunk is no longer the trunk, and is instead used for Gecko 1.9 / Firefox 3 and the 1.9.0.* / 3.0.* security releases."
The corresponding file in the current "mozilla-release" branch (which I presume includes 17, and it is the same as the "-esr17" branch) does not have that define, and that identifier does not appear in the release tree at all. The actual variable that's set here using the enum name (MAX_PIPELINED_REQUESTS) from nsHttp.h is
mMaxPipelinedRequests, and looking at the other references to that, its only restriction would seem to be that it's an unsigned 16-bit value, meaning it has a range of 0-65535.