Safari is lacking a bit on the devs end imo, inspector, while improved and also now featuring a responsive design preview, feels a bit laggy & unpolished, clicking on classes or IDs to copy them could be improved, increasing element dimensions/border/numbers with up and down keyboard arrows (after clicking on value) could be a good addition too and when you press the enter key while adding CSS properties to a class/id/element through the inspector the cursor sometimes break the property line into two words or jumps back up to the line where another property is, so I find this interesting and will give it a try.
If you have several pinned tabs and several conventional tabs open at the same time, managing them horizontally to the sides is lacking optimization (chrome or firefox handle this much better, they could use some ideas from here).
On a side note, I really don't get why they won't use favicons as pinned tab icons, as it is, favicons in the URL bar, are not even visible, unless you click on the URL bar while on active site.
The advantages of favicon to the actual pinned icons are immense:
-multicolor support.
-big help to visualize several tabs open (currently it's just text).
-no need to clear pinned icon cache folder consistently (which isn't very handy) for safari to show changes.
-no need to include another line of code (link rel="mask-icon").
-multi-platform support.
