Make sure you are not blocking content.

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?

One issue that seems more common lately is Firefox's Tracking Protection feature. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature: Tracking Protection {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. You may also lose any settings for that website.

• Cookies; Delete cookies to remove the information websites have stored on your computer {web link}

• Cache; How to clear the Firefox cache {web link}

If there is still a problem, 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). Did this help?

While you are in safe mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}

Done all the above, the issue is still there. Tracking protection mode is not active and also no content blocking as well. Cache cookies have been removed. Firefox was reinstalled with all the previous profiles/settings files deleted manually.No changes. Windows update was run, no new files to update. Any help is greatly appreciated.

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

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

Safe mode with the network support included worked fine. Firebox could open the windows no issues. So now how to find whats causing the issue?

NunoMagalhaes said

Safe mode with the network support included worked fine. Firebox could open the windows no issues. So now how to find whats causing the issue?

That tells us that it's not a Windows or FF issue but something is the case of the problem. So now you need to look at other installs you did to FF that might be the root of the problem.

It could be the work of one of your add-ons, or it could be Hardware Acceleration. How to disable Hardware Acceleration {web link}

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.