User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20171206182557 Steps to reproduce: Update to Firefox Quantum. Actual results: The width of open tabs and background color changed in a way that makes it difficult to recognize the icon and read the caption text in many tabs. The latter problem does not exist if only a few tabs are open. The first problem does not exist for favicons that are optimzed for dark background. See attached image. Expected results: Updates should not negatively affect usability of the browser. 1) Please set a reasonable background color that supports good usability. 2) Please set a minimum tab width that enables users to recognize the caption.

1) In Windows 10 at least, the Default theme takes on whatever accent color you picked in Windows. You can switch to the built-in Light or Dark theme, or you can install a third-party theme [1]. Something with a pattern might provide good icon visibility in all cases. 2) When you have many tabs open, they shrink so more of them fit on the tab bar. Chrome et al will shrink the tabs so much that the label is completely invisible, while Firefox will preserve some of it [2], enough so you can tell which page is loaded in the tab. I think the current default is fine for most, but you can argue otherwise on mozilla.dev.platform [3]. If you personally want more of the label visible, you can enter about:config into the location bar and change the value of browser.tabs.tabMinWidth. [1] https://addons.mozilla.org/firefox/themes/ [2] Bug 1406478 [3] https://groups.google.com/forum/#!topic/mozilla.dev.platform/4RAQOAMT9PI