Hi. I have developed a software. This software have property of localhost. The program works as follow. First: When User login localhost , The program read index.html as byte and the byte send browser with C# HTTPProcess class . The methot works Chorme , İE:) but doesn't work on firefox. Photo https://www.dropbox.com/s/5r7hh4rrj3jvoxl/Capture.PNG?dl=0 https://www.dropbox.com/s/awlengzrzk7tut3/Capture1.PNG?dl=0 I have searched this eror message whic be taken by firefox but I dont find anything. The character encoding of the plain text document was not declared. The document will render with garbled text in some browser configurations if the document contains characters from outside the US-ASCII range. The character encoding of the file needs to be declared in the transfer protocol or file needs to use a byte order mark as an encoding signature. I am wainting yours helps. Thanks