User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:2.0b9pre) Gecko/20101223 Firefox-4.0/4.0b9pre Build Identifier: Mozilla/5.0 (X11; Linux x86_64; rv:2.0b9pre) Gecko/20101223 Firefox-4.0/4.0b9pre When you have many tabs open and you click on the close button to close one of them, all the tabs get slightly larger to fill up the tab bar again. This is bad, because the tabs are shifting around right under the user's mouse. The tabs should not change size until the mouse leaves the tab bar. This makes it easier to close several tabs in a row. Tabs should never change their dimensions while the mouse is inside the tab bar. The only possible exception is closing the rightmost tab, in which case expanding the other tabs to fill probably makes sense. Reproducible: Always Steps to Reproduce: 1. Open many tabs. 2. Click any tab's close tab button except the last. Actual Results: The tabs resize to fill in the gap left by the deleted tab, making it impossible to predict where the other tabs will be after closing the tab. Expected Results: All the tabs to the right of the closed tab should have shifted one tab-width to the left, without any tabs changing size, thus leaving a space as wide as the closed tab on the right end of the tab bar. Once the mouse leaves the tab bar entirely, the tabs should expand to fill the space.
This delayed resizing feature is present in Chrome. Here is an article with lots of pictures that demonstrate why this feature is awesome: http://www.theinvisibl.com/news/2009/12/08/a-piece-with-a-lot-of-screenshots-about-the-close-tab-behaviour-in-google-chrome/
Known issue. May make it into Firefox 4.