Try changing your home page, How to set the home page

Yes I've tried it but it doesn't solve my problem.

And if I access Firefox from the file location it will open my normal homepage. But if I enter Firefox from start menu, task bar, and shortcut it will enter [file:///C:/Program%20Files%20%28x86%29/Mozilla%20Firefox/] page.

You can check the target line in the Firefox desktop shortcut (right-click: Properties) to make sure that nothing is appended after the path to the Firefox program.

Open a new window or tab. In the address bar, type about:config. If a warning screen comes up, press the Be Careful button. This is where Firefox finds information it needs to run. At the top of the screen is a search bar. Enter browser.newtab.url and press enter. browser.newtab.url tells Firefox what to show when a new tab is opened. If you want, right click and select Modify. You can change the setting to;

about:home (Firefox default home page), about:newtab (shows the sites most visited), about:blank (a blank page),

or you can enter any web page or about: page you want.

The same instructions are used for the new window setting, listed as browser.startup.homepage.

For reference, here's a screenshot of the Properties dialog for my Firefox program icon, showing the Target line. Does yours match?

Match exactly.

The next time you start Firefox, could you start it up in its Safe Mode? That's a standard diagnostic tool to deactivate extensions, some advanced features, and some custom settings. More info: Diagnose Firefox issues using Troubleshoot Mode.

You can start Firefox in Safe Mode by holding down the Shift key when double-clicking the Firefox icon.

A small dialog should appear: click "Start in Safe Mode" (not Reset).

Any difference?

Note that a stray dot (.) appended to the target line can cause this issue, so you may have to give this another check.