PHP,Why doesn't the page load when I send an image about 900KB?

I have a form in PHP to upload two images. I can upload files about 400KB perfecty, but when I try to upload files over 900 KB, it throws the message "PR_CONNECT_RESET_ERROR" in Firefox. I tried using Chrome, Opera, but it is the same thing (it do not load the page). I checked the configuration in php.ini and everything seems correct.

upload_max_size= 8M;

post_max_size= 8M;

memory_limit= 8M;

max_execution_time= 300;

I don't understand why this happens. Any ideas? Thanks.