Hi. To remove it or simply change the location of the download button, right click on somewhere in your Firefox bar (next to tabs) then click on "Customize". If you only want to hide the download icon then click on it and drag it from the toolbar to the window with the Firefox icons. If you want to change its location then simply drag it to anywhere else in the toolbar.

Firefox 20 changed from the old Download Manager to a new Download Panel. You can find a complete write-up here: Where to find and manage downloaded files in Firefox.

I suggest keeping that arrow around since it provides handy notifications. You can use the Customize feature to drag it down to the add-on bar where it won't take up as much space. To start customizing:

• right-click a blank area of the tab bar > Customize
• tap the Alt key > View menu > Toolbars > Customize

If you really don't need it, just drag it to the Customize dialog. You can always come back for it later if you like.