First, some of the duplicates may be in the collected address book. One possibility is to delete those entries. For the others, my approach would be to export as csv file and then use a spreadsheet program to use its various tools to achieve the goal. It's not easy, but doable.

Hi David, Thanks for the quick reply. However when I select export from either of two places, the only places it appears, it either only allows a zip file or an ical file. Following the instruction link you referenced I cannot see on my version where it allow me to select a csv format. To that I'm clueless?

Also when I select the full export to a zip file it appears that the exported files are a database format only not readily processable.

Any other ideas?

click to addressbooks, then highlight the desired addressbook. there are three dots to the right of the name. Click that and it is a drop-down menu with export to csv option.

hi i've exported an address folder to csvfile. opened with both apache openoffice & planmaker - neither of these work - first the columns are mixed up, more with openoffice than planmaker. after sorting that out & selecting the email address column the data/filter/delete duplicates features do not work ?????? rgdschris

also, why does tbird 115.11.00 NOT have a 'delete duplicate' option as standard????????????????????????????

On the spreadsheet approach, a pivot table might clear up the dupes. On the other question, removing duplicates has not been a major user issue. However, maybe the issue just needs more visibility. You can go to connect.mozilla.org and in the IDEAS area, you can post your recommendation. Developers see suggestions there.