User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0a1) Gecko/20120123 Firefox/12.0a1 Build ID: 20120123095741 Steps to reproduce: Close a tab either by clicking on the cross/close button on the right corner, or pressing middle mouse button on tab bar. Actual results: 1. The title text disappears. 2. The close button moves to the left end of the tab being closed 3. Tab's width starts decreasing until it reaches the width of the close button. 4. Close buttons disappears. 5. Tab's width reduces to 0 and then tab disappears Expected results: Step 4 should just happen along with step 1. or even before it. In the current situation, the closing animation gets jittery while removing the close button. If the button is not present, the animation would be smooth throughout.

Can you reproduce this in safe mode? In a new profile?

Not in new profile, but in safe mode, with add-ons disabled, even though the close button does not shift to left, and just disappears, there is a jerk at the same point, as if the close button existed and now was being removed. Well, may be it is on my own system only. Just wanted to discuss about this issue with people concerned so filed a bug

We need to narrow down why this is happening in safe mode. Can you attach your about:support output?

Application Basics Name Firefox Version 12.0a1 User Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0a1) Gecko/20120123 Firefox/12.0a1 Profile Directory Open Containing Folder Enabled Plugins about:plugins Build Configuration about:buildconfig Crash Reports about:crashes Memory Use about:memory Extensions Name Version Enabled ID Auto Complete 1.2 true AutoComplete@girishsharma FireGestures 1.6.7 true firegestures@xuldev.org Greasemonkey 0.9.14 true {e4a8a97b-f2ed-450b-b12d-ee082ba24781} Open Bookmarks in New Tab 0.1.2011120101 true openbookmarkintab@piro.sakura.ne.jp Proxy Selector 0.80.6 true proxyselector@mozilla.org Stylish 1.2.5 true {46551EC9-40F0-4e47-8E18-8E5CF550CFB8} UI Enhancer 3.1 true UIEnhancer@girishsharma WordWeb one-click lookup 5.0.1701 true wcapturex@deskperience.com Firefox Synchronisation Extension 1.7.56.205 false fe_7.0@nokia.com RealPlayer Browser Record Plugin 14.0.5 false {ABDE892B-13A8-4d1b-88E6-365A6E755758} Important Modified Preferences Name Value accessibility.typeaheadfind.flashBar 0 browser.places.smartBookmarksVersion 2 browser.startup.homepage http://www.facebook.com/|www.igoogle.com browser.startup.homepage_override.buildID 20120123095741 browser.startup.homepage_override.mstone rv:12.0a1 browser.tabs.homeTab true browser.tabs.loadBookmarksInBackground true browser.tabs.loadDivertedInBackground true browser.tabs.warnOnClose false browser.tabs.warnOnOpen false dom.min_background_timeout_value 4 extensions.checkCompatibility false extensions.checkCompatibility.10.0 false extensions.checkCompatibility.10.0a false extensions.checkCompatibility.11.0 false extensions.checkCompatibility.11.0a false extensions.checkCompatibility.3.6 false extensions.checkCompatibility.3.6b false extensions.checkCompatibility.3.6p false extensions.checkCompatibility.3.6pre false extensions.checkCompatibility.3.7a false extensions.checkCompatibility.4.0 false extensions.checkCompatibility.4.0b false extensions.checkCompatibility.4.0p false extensions.checkCompatibility.4.0pre false extensions.checkCompatibility.4.2 false extensions.checkCompatibility.4.2a false extensions.checkCompatibility.4.2b false extensions.checkCompatibility.4.2p false extensions.checkCompatibility.4.2pre false extensions.checkCompatibility.5.0 false extensions.checkCompatibility.5.0a false extensions.checkCompatibility.5.0b false extensions.checkCompatibility.5.0p false extensions.checkCompatibility.5.0pre false extensions.checkCompatibility.6.0 false extensions.checkCompatibility.6.0a false extensions.checkCompatibility.7.0 false extensions.checkCompatibility.7.0a false extensions.checkCompatibility.8.0 false extensions.checkCompatibility.8.0a false extensions.checkCompatibility.9.0 false extensions.checkCompatibility.9.0a false extensions.lastAppVersion 12.0a1 gfx.content.azure.enabled false network.cookie.prefsMigrated true network.http.spdy.enabled true places.database.lastMaintenance 1327345269 places.history.expiration.transient_current_max_pages 20723 places.history.expiration.transient_optimal_database_size 39556136 privacy.cpd.cookies false privacy.cpd.downloads false privacy.cpd.formdata false privacy.cpd.history false privacy.cpd.sessions false privacy.donottrackheader.enabled true privacy.popups.showBrowserMessage false privacy.sanitize.migrateFx3Prefs true privacy.sanitize.timeSpan 0 security.dialog_enable_delay 10 security.warn_viewing_mixed false webgl.msaa-level 4 Graphics Adapter Description NVIDIA GeForce GTX 260 Vendor ID 0x10de Device ID 0x05e2 Adapter RAM 896 Adapter Drivers nvd3dumx,nvwgf2umx,nvwgf2umx nvd3dum,nvwgf2um,nvwgf2um Driver Version 8.17.12.9053 Driver Date 12-17-2011 Direct2D Enabled true DirectWrite Enabled true (6.1.7601.17563) ClearType Parameters ClearType parameters not found WebGL Renderer Google Inc. -- ANGLE (NVIDIA GeForce GTX 260) -- OpenGL ES 2.0 (ANGLE 1.0.0.930) GPU Accelerated Windows 1/1 Direct3D 10 AzureBackend direct2d

Is this what you see? http://dl.dropbox.com/u/34104919/20120501_001230.mp4

(In reply to Marco Castelluccio [:marco] from comment #5) > Is this what you see? http://dl.dropbox.com/u/34104919/20120501_001230.mp4 Not really, currently I am unable to reproduce it, so closing