Is there a reason you are using an old version of Firefox?

Download Firefox Full Installer For All languages And Systems {web link}

Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences<Enter> in the address bar.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

That specific error code is somewhat rare in forum threads. Past solutions may have included (sometimes it's hard to tell which suggestion helped):

• Disabling Firefox from using IPv6 (see that topic in: Firefox can't load websites but other browsers can)
• Checking for a proxy setting in the Options dialog: "3-bar" menu button (or Tools menu) > Options > Advanced > Network mini-tab > "Settings" button -- try "No Proxy"
• Fixing a flaky internet connection
• Removing some extensions (e.g., MaskMe and an old version of DoNotTrackMe)

I discovered my web filter Net Nanny was causing the problem. When disabled, the downloads work fine!!