Here is a PCIe Firewire adapter that will fit into PCIe x1 slot of your OptiPlex 3010.  Note that it has a low profile bracket that can be used for installation to your SFF desktop. 

Thank you for your quick reply :-) 

Re: PCIe version 2 slot

I think OP meant PCI Express Gen. 2.0 X1  in 3010 for add in card

New Dell PCIe 1394AB workstation capture card control card JGXNJ | eBay

PS 

the Full height (FH) PCIe Dell oem 1394 include

Re: I have already bought 2 but they do not fit the slot :-(  

OP did you purchase by accident old PCI card (I see quite a few PCI 1394 cards) like this

in terms of speed of 1394 ab card in PCIe x1 gen 2 slot:

they are compatible:

@redxps630​ Yes the cards I bought are both like that, on the face of it they look like they fit but they are approx. 1/8th inch too long & the "key" is in the wrong place.

@redxps630​ Do you have an image of the type of card I need to fit ... it's all so confusing for me :-)  Lol

You bought the old PCI cards and not the PCI express cards. PCI card only fits white PCI slot in older pc. Your pc does not have white PCI slot. You need to get a PCIe (e for express) x1 (1 for one lane) 1394 add in card. The one I recommended from Dell is a good fit for your pc’s short black PCIex1 slot.  This one is new open box from a reputable vendor.

https://www.ebay.com/itm/354077385575?

PS you cannot install old PCI card in the long black PCIe x 16 slot (16 for 16 lane) in your pc either. They are completely incompatible.

Sample image

@redxps630​ Once again thanks for your help, and patience :-) 

Unfortunately i'm in the UK and the seller is in the USA and doesn't ship to the UK or the costs are too high. But I have located one here in the UK now. Thank you for your help :-)

regards Graham