Hosts File Blocking Install?

I cannot install Flash Player in Firefox V4 Mac OSX 10.6.6. (OSX 64bit)

I download OK.

Flash Reader LOOKS like it installs but it doesn't.

No Success message is seen.

Flash content unavailable.

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Why did I need to install Flash Reader? Wasn't it always installed on Firefox?

When I opened a web site that required flash player.

I could not see the mandatory Flash content.The web site prompted me to install Flash Reader.

I tried the install.

The install failed.

I was dumped into troubleshooting web pages from Adobe.

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What has changed that may be problem?

I installed many "blocked" URLs/IP addresses in my /Private/ETC/Hosts file.

I also upgraded to Firefox V4.

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I have Safari browser in addition to Firefox.

Safari's Flash Reader works OK.

When I opened the same web site (described above) using Safari, Flash worked.

Possible Cause #1:

This might be the result of something in my ETC/HOSTS file blocking communication

with Adobe that is required for install. I don't want to delete my hosts file of course.

I don't know if communication with Adobe is required (after OK download) for install.

If I knew what URLs  must be contacted as part of the install process, I can modify the HOSTS file to accommodate.

What URLs. IP addresses etc. must I permit to complete the install of Flash Player?

Possible Cause #2

Prior to my install of Firefox V4, Flash Reader worked OK. Could problem be associated with V4?

Flash Reader works OK using Safari browser on same computer.

I have not tried to uninstall and then install Flash Reader on Safari to see if Safari has the same install problem.

I don't wish to lose use of Flash on Safari too.

Attempts to fix:

Multiple Downloads, installs and uninstalls of both the 32 bit Flash Reader and the Beta 64bit Flash Reader.

Comparing behavior of Flash on Safari browser.

To Rule Out Cause #1:

Is communication with Adobe is required (after OK download) for install?

If yes, what URLs/IP addresses must be permitted?