(optional) support for clearing duplicate bookmarks

I'll preface by saying that this feature absolutely should be optional -- Firefox doesn't prevent from creating duplicate bookmarks and users can for instance recreate ones in the toolbar for organization purposes. Clearing duplicates by default would be destructive. I recommend adding a clear warning, similar to the one recommending creating a bookmark backup.

Personally I have loads of redundant duplicates after updating everything to HTTPS, clearing UTM parameters and the Firefox reader mode URLs.

May fit between 'replace domain' and the regex tabs:

[MrOtherGuy]

I can see how deleting duplicates could be useful, but I would guess there are already existing extensions for specifically that purpose. But I'll consider this.

I really don't want to add it into the update process, so it should be it's own "tab" so that you can run remove duplicates separately.

It would also need it's own control UI, silar to selecting which boolmarks to update ala v1.0 checkboxes because one needs to be able to select which of the duplicates to keep.

I really don't want to add it into the update process, so it should be it's own "tab" so that you can run remove duplicates separately.

This is what I tried to suggest.

It would also need it's own control UI, silar to selecting which boolmarks to update ala v1.0 checkboxes because one needs to be able to select which of the duplicates to keep.

Agreed.