I am currently very dissatisfied with every browser available for OS X (a Mac). A firm requirement for any browser I use is that there is a version of Last Pass for it. This limits my choices to just four options:
Firefox Has been my mainstay for years on all platforms. But the current incarnation on OS X keeps eating memory. I have 32 GB of memory on my Mac Pro, but OS X starts swapping out parts of Firefox when the memory use gets about 1 GB or so. The problem is that some pages I use refresh themselves, and apparently Firefox is not smart enough to drop the old pages. Example sites are Weather radar displays on http://wunderground.com, and The Wall Street Journal (http://online.wsj.com). Firefox memory use gets well above 3 GB (with no end in sight), but by the time it gets to 1.5 GB or so, it is so slow that I have to restart it.
Update: Firefox seems to have fixed its memory issue, and is again my default browser.
Chrome is alas 32-bit only, so you cannot use Java on OS X, a big problem. Also, its bookmark system makes it really hard to file a new bookmark since every folder is fully expanded.
Opera 16, 17, 18 use the Google Chrome engine, so are also 32-bit only. In addition, they decided to remove bookmarks altogether. There is a plugin called "Bookmark Manager," but it is hard to file new bookmarks.
Safari is the only browser in existence that does not let you set a location for each downloaded file without jumping through many hoops. It is also really hard to find plugins since there is no search facility. When I try to search for any on them, I get sent to the iTunes store. Finally, all the extension icons are shades of grey, which makes it hard to tell the status of some plugins (e.g., Last Pass, which turns red when you are logged in).