A Safari window can get crowded. This means the tabs get shrunk down to a width of 120 pixels. That’s about enough room for 12 letters and the elipsis, which is sometimes enough text to divine the contents of the tab, but oftentimes not.
What would help is a Tooltip on hovering. Chrome does this:
Chrome also trumps Safari in showing the website’s favicon, as can be seen in the two images above. I guess that favicons were removed from Safari tabs (version 8 onwards) because they can be ugly and don’t fit the monochrome greyness of OS X’s graphite theme. Like colours in the Finder sidebar, I think this is a case of form over function.
Safari 9.1.2 (11601.7.7); OSX El Capitan 10.11.6.