Will it duplicate? Probably.
"Sometimes" I've noted that a re-import doesn't duplicate, but only because the forms were really exactly the same. A manually entered form will always be different in subtle ways, and the software cannot know that they are really supposed to be the same form.
You can always delete the duplicate form, but you do have to pay attention to each form's table of what's been entered.
You can import your Fidelity 1099-B. If you're not able to import your 1099, you can always enter it manually. Select I'll type it in myself or Skip Import and proceed.
TurboTax 1099 partner list.
What if I can't import my 1099? Please see this FAQ before importing.
Will it duplicate? Probably.
"Sometimes" I've noted that a re-import doesn't duplicate, but only because the forms were really exactly the same. A manually entered form will always be different in subtle ways, and the software cannot know that they are really supposed to be the same form.
You can always delete the duplicate form, but you do have to pay attention to each form's table of what's been entered.