1. i come from safari where i command click on a link to make a new tab. i can do this in firefox but i find i hold down command key and all of a sudden the text shrinks way down or blows up to incredible size because command key and scroll wheel on mouse means change the text size on firefox. this does not happen in chrome or safari. it is a problem.
2. a very useful command on safari is command z (undo on mac). so, if you delete a tab then command z and boom the tab reappears. this happens often and it's very useful. you can do command z a few times if you delete 3 or 4 tabs and and so get back to the tab you want.
i like a lot of things about firefox but mainly it feels solid. there are problems with safari.