There are alot of different reasons that Firefox could be starting slowly (and 3 seconds from a cold boot isn't horribly slow, it takes 2-3 seconds on my SSD with 24 GB of RAM and i7).

You can try to create a fresh profile to see if it starts faster. Profile Manager - Create, remove or switch Firefox profiles

Try to update your graphics driver. Upgrade your graphics drivers to use hardware acceleration and WebGL

Do you have the same home page set to start up? If you have a more graphics/flash heavy webpage it can take Firefox longer to be usable than a simple HTML one. Or if you have multiple tabs being opened you might want to try only loading them as needed. (Go to Options, Tabs, check "Don't load tabs until they are selected").

Make sure Windows is fully up to date on both machines

Make sure plugins are updated. https://www.mozilla.org/plugincheck/

Do you have the same security software?

Other programs running can also interfere with startup time.

So in short, there is no easy answer (and don't use registry cleaners, they only make things worse)

Which security software (firewall, anti-virus) do you have?

Some security software has virtualization or sandbox features that may cause problems by protecting and restoring files in the Firefox profile folder.

A possible cause is security software (firewall,anti-virus) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/kb/Server+not+found
• https://support.mozilla.org/kb/Firewalls

I have done this:- Deleated firefox and all personal options. Restarted the computer and installed firefox. Now I configure the startup website tho my own. Close firefox and start it again. It is now up again after 0.5 sek. I do close and restart several times with the same result (0.5sek). Now I loggout and loggin from inloggscrean in windows. When the computer is reade I start firefox. Now it take 2.5 sek (Cold start). I close firefox and start it again. Now it toke 2.5sek (warm start). And restart firefox again and again with same 2.5 sek to start upp. Why is that?

Yes I have the same startupp webpage in all my test. Yes I have uppgrade all my plugins Yes I have upgrade the grafics driver Yes Window is up to date

I use Windows Security Essensials and yes it is updated.

No there are no other program running during the tests.

I have disable my firewall with the same result as described above

So I have done all youer suggestions and the uppstart is still 2.5 sek. in all my other tested computer there are the .5 sek upstart time in all I just described above. Now delay there.

I think Firefox do something in logons sequence that slow down the upstart of firefox. Why is there no difference between the cold startup and warm startup of Firefox?

How do I uninstall my plugins? Yes I can dissable them but want to uninstall instead.