This is the thing. If I develop a site and use Chrome to perfect layout, css, etc. then I know when I open Firefox, it'll work the same. Every once in a while, I'll miss a prefix and Firefox will act poorly, but it's very rare, especially with Autoprefixer. Same thing when I test in IE10 and 11, save for a few details (a few 3D CSS Transitions / properties don't work, etc.)
When I do open Firefox or IE11 or 10, and something looks wonky, I almost immediately know what it is. When I open Chrome on my phone, it works as expected. It is obvious that X issue is causing Y effect for Z reason.
When I open Safari, it's like A is causing Z, X has no effect whatsoever even though it seems it should, and Y is over there with C, D, and E cuckolding in the corner laughing at my frustration.
I can fix all those bugs and then when I open Safari on my iPhone (4, 5 and 6), there are new issues. Issues that aren't in the browser are on the phone. Issues that are on the phone aren't in the browser.
It may be because they are behind on the times. But they are also implementing the spec wrong in some cases. Flexbox was implemented (via webkit) for a while now but hasn't been updated and therefore the new, right way to do it is being held back and other browsers are following a lead that does NOT follow the fucking spec. You want to see the future awesomeness of this layout thing that is supposed to save our life and kill the floating ways of the web?! Seriously?
Furthermore, there are just inconsistencies that seem to be like someone forgot to flip a switch rather than not following the spec or being behind on the times. Weird sizing issues regarding SVG (that work in ie9) are a problem. Things that should not be an issue.
The other issue is at least with IE you had ie7. You had ie8. You tested, you put in some ie headers and you at least knew you were good on ie8 or ie7 or whatever. It didn't matter if you were ie8 on windows xp, windows 7, or a mac emulated version.
Things are different in Yosemite vs Mountain Lion version of Safari. Even though its the same Safari version, supposedly. Right now, I'm fighting with a font issue that appears only in Yosemite safari, but not in ANY OTHER VERSION OF SAFARI. This is impossible to test. I'm messaging everyone in my life to figure out who's seeing what and I HAVE 4 MACS ON THE DESK IN FRONT OF ME.
Chromes not perfect. Firefox isn't perfect. But Safari is quickly turning into a beast I would rather not deal with. Operating Systems should just stop inventing fucking browsers.