You can try to disable SPDY in Firefox.

Try to set the network.http.spdy prefs to false on the about:config page.

• network.http.spdy.enabled
• network.http.spdy.enabled.v2
• network.http.spdy.enabled.v3

You can also check the other network.http.* and make sure that they have the default values.

• http://kb.mozillazine.org/about:config

I read this recommendations in Support Pages and follow the instructions for the first point: Set false to network.http.spdy.enabled, and nothing happened. Firefox Support can't create a patch to fix this issue ? I had to download Chrome but I like Firefox.................

You need to set all three SPDY prefs that I posted above to false.

Set all three SPDY to false and didn't work. What I should I do now: I put all three back to true ? or let them false ?

I'm almost crazy with this issue. I don't know what to do.....

See also this thread: [/questions/930282]

Create a new profile as a test to check if your current profile is causing the problems.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

You can also try to uninstall and reinstall Firefox and make sure that security software (firewall, anti-virus) isn't blocking the attachments.

Try to boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.