Cannot access Mozilla sites much of the time

Hello:

I use Firefox 2.0.0.8 as well as IE 7

I seem to have no problem connecting to internet sites.

However, I'm often unable to connect to the sites:

http://www.mozilla.org/

https://addons.mozilla.org

https://addons.mozilla.org/en-US/firefox/extensions/

and I'm told that the connection has timed out.

My internet connection is DSL via a Linksys router

These connection problems occur in IE 7 as well when I'm unable to connect
via Firefox, which is my default browser.

When those sites are inaccesible, I'm also unable to update Firefox Add-ons
via:
Tools-->Add-ons-->Find Updates ,

The process often hangs with errors while trying to find the updates.

I've tried disabling my Zone Alarm firewall, and re-enabling the built-in
windows XP Firewall, but this doesn't change matters.

These problems occur most of the time I try to connect to these sites or
update the add-ons. But at other times, they work fine.

Any ideas here?

Thanks in advance:

-Eli

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Windows XP Professional Edition

Zone Alarm Security Suite 6.1.744.001

Firefox 2.0.0.8

IE 7