javascript:(function(){window.location.href = "https://dev.lemmy.ml/create_post?title=" + encodeURI(window.document.title) + "&url=" + encodeURI(window.location.href);})()

make a bookmark with that. it will populate the page title, but since it doesn’t submit – just navigates you to that page – you can change it however you want before you submit. Real easy :) I am going to test it out to see if I can get it to work well enough on android to substitute for a proper native share intent option.