I'm not familiar with the extension, and assuming that you do want the extension, did you check the options for the extension in the Add-ons Manager ("about:addons"), and the homepage listed for the add-on if you obtained it from addons.mozilla.org/

You can't remove it by drag and drop in customize toolbars because it is only for Firefox components, not 3rd party extensions.

I am sorry, either you need to un-install the extension using the Add-ons Manager or contact Freemake. You can also look out if you can disable that button by going to Add-ons manager and selecting Options button FOR Freemake extension.

@Swapnilrustagi

Not entirely true. Many extensions "drop" buttons in the Customize Palette, and the user can move toolbar buttons into there, too. Not a limitation of Firefox; if it won't "drag" into the Palette from a Toolbar, it's the fault of the individual extension being deficient. See the screenshot - almost all the buttons that are showing are from extensions that I installed. And if you look carefully you'll see that extensions can modify the Palette in ways beyond adding buttons to the Palette.

@the-edmeister, maybe, I am not as experienced as you. And nowadays I am using Opera. I am still on Mozilla support to help people who need support.

Maybe extensions can do that. But I think few (popular ones). Of course few from 6500+ extensions means some 500-800 extensions.