i was having this issue in boost for long time. Once activated normal performance, the first time which you open the web, any url which you open seems broken. Firefox says (sorry spanish):

Error de codificación de contenido

La página que está intentando visualizar no puede mostrarse porque utiliza un formato de compresión no válido o no admitido.

* Por favor, contacte con los propietarios del sitio web para informarles de este problema.

and, in Safari:

"cannot decode raw data (NSURLErrorDomain: -1015)

the solution which i´ve found is to check this option:

Do not cache if php error on page

at least by the moment, i still have sometimes this error, allways opening the first time some url or after making a clear cache ¿?¿?