By default, Polipo does not use Poor Man’s Multiplexing (see Poor Mans Multiplexing). If the variable
pmmSize is set to a
positive value, Polipo will use PMM when speaking to servers that are
known to support pipelining. It will request resources by segments of
pmmSize bytes. The first segment requested has a size of
pmmFirstSize, which defaults to twice
PMM is an intrinsically unreliable technique. Polipo makes heroic efforts to make it at least usable, requesting that the server disable PMM when not useful (by using the ‘If-Range’ header) and disabling it on its own if a resource turns out to be dynamic. Notwithstanding these precautions, unless the server cooperates6, you will see failures when using PMM, which will usually result in blank pages and broken image icons; hitting Reload on your browser will usually cause Polipo to notice that something went wrong and correct the problem.
More precisely, unless CGI scripts cooperate.