I don't think this can be done efficiently. (Like certainly it would be possible to on the php side, look through all the contribs we're about to output, and remove duplicates. However if a person edited a page once, then edited again 20 000 edits later (so that the two contribs are not on the same page when going through special:contribs 50 contribs at a time), it would be very difficult to make it so only one of those appeared.

smjg wrote:

How does it do "Only show edits that are latest revisions" efficiently enough? Maybe knowing the database structure would help to put it in better perspective.

Database structure is documented at [[mw:Manual:Revision_table]] and [[mw:Manual:Page_table]]. Only show latest edits does an inner join from revision table to page table on rev_id = page_latest .

I've mentioned this on enwp (and other places -- "my" script works on explainxkcd for example), but for a workaround reference on phabricator, my [[User:Markhurd/hidetopcontrib]] script can do this, effectively doing what Bawolff suggests at the JavaScript/html level.