Were you starting Firefox while the computer was booting up? All computers, during boot up, have a bottleneck problem because of all the programs being loaded.

If this is the case, wait about 30 seconds for the computer to finish booting.

If not,

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding

https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-ram

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

- This occurs long (minutes/hours) after booting up. Anytime I try and start firefox fresh, If there is at least one firefox instance/window open, any requests for a new window are relatively instantaneous. It is only when I am initiating a new firefox window when no others are running. e.g. After using firefox, and closing all windows/instances of it, the next time I try and start firefox again it takes 25+ seconds to start (blank screen) and then another 25+ seconds to load that first page.

- Tried safe mode. No change in startup/load time.

- Resource usage at a minimum. Task manager reports (For all processes while firefox is starting or running) that I'm using less than 4% of CPU, only 4GB of 32GB Ram, minimal disk and network utilization. Bringing up firefox does not cause any resource to spike. It just takes forever to start and load the first page.

Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

I don't know if it is relevant to you, but a recent Avast/AVG update created severe performance issues for Firefox users. If you use either of those programs, please trigger an update to rule out that issue.

FredMcD said

Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there? http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Ok. Starting my computer in safe mode with networking allows firefox to start up and load immediately. So now the question is why is it ONLY firefox that has a problem when running in normal bootup mode? No problem with Chrome nor Internet Exploder nor any other application, whether it uses the internet or not. PS It has nothing to do with one website nor another. It takes firefox 25 seconds to start, no matter what website I have listed as my startup selection, and it takes another 25 seconds to load whatever website I have selected. And no, I will not switch to Chrome. Tried it. Don't like it.

This may be caused by your protection programs. What programs are you using? As a test, disable one or another.

I not only tried disabling Norton, but I also tried uninstalling it. No change in the time it takes for firefox to start up. My anti-virus is not the problem. And again, why is it I ONLY have a problem with firefox??? All other applications work as expected, including chrome and internet exploder, MS office, Steam, .....

Noted in task manager that when I select firefox, one and only one instance of firefox shows up in running processes. 25 seconds later when the blank window show up, three more instances show up. 25 seconds later when the firefox gets populated, one more instance of firefox show up for a total of five instances running for one window. If I open another window, one more instance of firefox shows up.

Then another of the programs is causing the issue. What programs are normally running on your system?