On my Linux Ubuntu system with Firefox 17.0.1 (and with several earlier releases, eg 12-16 I think) after a few weeks the tab triangle or arrowhead on one or more Firefox windows becomes defective. This problem is different from http://support.mozilla.org/en-US/questions/931515 in that if I restart the browser and resume the Firefox session the problem goes away for a while. (Note: I will wait until 05:00 UTC on 28 Dec before restarting FF to clear the current instance of the problem, in case anyone can suggest other relevant tests or data.)
The main symptoms are these: Triple click no longer slides the list of tabs all the way left or right. Double click appears to work once (from an extreme end). Single clicks step the tab list one tab at a time up to near an extreme end but then stop working before the extreme tab becomes visible. The following paragraphs give some more details about the symptoms.
When the problem occurs, tabs for new pages (eg reached by links from the right-most visible tab and opened in new tabs) do not become visible (that is, are not squeezed into the list on the tabs bar). The right-facing triangle, although not grayed out, does not make the tabs for the newly opened pages visible, but seems to have no effect. Clicking the X for the right-most visible tab closes that page and then one of the tabs that are "hidden out to the right" becomes visible, but other tabs out to the right remain inaccessible.
Meanwhile, the tab triangle arrowheads continue to work ok on other FF windows. For example, the left and right tab triangles in this current FF window (where 15 tabs are visible for 17 pages open in the window) are working fine. But in the FF window with the problem (where 15 tabs are visible for 40 pages open in the window) the triangles stop working one tab too soon: they don't give access to the leftmost or rightmost tab.
Note, clicking + (Open a new tab) jumped the list to the right end, with the new tab and an empty page visible; but after I clicked the left triangle three times, so that the new tab scrolled off to the right, no matter how many times I click the right triangle, that tab remains invisible, even though the webpage for it is still visible as the currently selected page. Opening a URL from command line acts the same way.
The system runs Linux 3.2.0-35-generic #55-Ubuntu 12.04.1 LTS x86_64 system with Firefox 17.0.1. I don't remember when I first encountered the problem but believe it was in 2011 (vs 2010) on a Fedora 7 system. Restarting FF has always cleared the problem. The command line "echo session $DESKTOP_SESSION desktop $XDG_CURRENT_DESKTOP; wmctrl -m" produces (in part)
session ubuntu-2d desktop Unity Name: Metacity
"top" shows, in part:
PID PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 3033 20 0 2158m 1.1g 38m S 7 28.7 3878:21 firefox
Note, I snipped 1200 lines of text from the Troubleshooting Information because the 50000 bytes in it pushed this post's length over the 30000 byte limit. All of the snipped lines started with "print.tmp.printerfeatures"
Does the scroll wheel still work if you hover the mouse on the tab bar?
Does it make any difference if the tab bar is on top (browser.tabs.onTop)?
This issue can be caused by an extension that isn't working properly.
Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).
(all those print prefs aren't really important; I don't know why they are all included in the list as we hardly ever use them)
I don't remember if the scroll wheel works (to shift line of tabs, with mouse hovered on the tab bar) when the problem occurs, but when the problem recurs in a few weeks I will test that out. (I restarted firefox 12 hours ago to clear the problem.)
Is there a way to move the tabs bar without restarting? I've lost track of how I selected the prefs.js setting `user_pref("browser.tabs.onTop", false);` (which I use because I am used to looking for the tabs bar just above the displayed page). If I can move the tabs bar without restarting, I'll move it and see if that makes a difference, when the problem next occurs.
If you change the browser.tabs.onTop pref on the about:config page then you should immediately see the change. You only need to restart Firefox to see that choice in the menus without a check mark if the tabs are not on top.
Ok, I clicked the browser.tabs.onTop line on the about:config page, and changed tab line position back and forth (ie the tab line moved up or down on alternate clicks) so I know how to change it for testing if/when problem recurs.
I don't understand which menus you are referring to in the 2nd sentence, since I haven't seen a preferences menu with a check box for browser.tabs.onTop preference.
Did you close and restart Firefox yet?
That is necessary to get the item to appear in the toolbar context menu and in View > Toolbars
The tab bar will move immediately to it's position just above the browser window, but the menu entry requires a restart like I wrote above.
Current Firefox versions only show the "Tabs on Top" menu entry in the "View > Toolbars" and "Firefox > Options" menu and in toolbar context menus if the tabs aren't in the default position on top.
I haven't closed and restarted Firefox since doing so at 06:00 UTC on 28 Dec to clear the problem. In any case, the "Tabs on Top" option shows up ok when I right click on Tools or when I click View and move to Toolbars; I didn't know where to find the option, but now know - thanks!
Are you counting 17.0.1 among "current Firefox versions", or not? (Ubuntu 12 hasn't pushed FF 18 yet.) Anyhow, I'm not sure how to interpret "Current Firefox versions only show the "Tabs on Top" menu entry ... if the tabs aren't in the default position". With 17.0.1 the entry shows up in View/Toolbars and Tools-context regardless of tab line position. The menu entry shows up with a check mark when the tab line is at top, and without a check when it's at bottom of toolbars.
I don't know how to get to a Firefox/Options menu; I use Edit/Preferences to set options. The Tools menu does not show an Options button.
Firefox 18 is scheduled for release on Jan 6 2013, so isn't included in current releases on the release update channel.
The Tabs on Top entry stays in the menu as long as Firefox is running and Firefox was started with the tabs not on top.
That menu is only updated when you restart Firefox, so to make it appear you need to set the browser.tabs.onTop pref to false and close and restart Firefox.
That menu entry stays in the menu as long as you do not close Firefox when the tab are on top and a subsequent would start Firefox with the tabs in the default position on top.
The problem has recurred (one week after restarting firefox) so I was able to test if the scroll wheel works to move to end of tabs and to test the effect of browser.tabs.onTop. In following, "tab" refers to a labeled box in the tab line among the tool bar lines. (43 tabs open in the problem FF window; 9, 18, and 24 tabs open in other FF windows working ok)
Summary: (1) Scrolling in the tabs can scroll to first and last pages but their tabs don't become visible. (2) tabs.onTop doesn't fix the problem although with first or last page selected when tabs.onTop is toggled, its tab becomes visible, but problem remains, ie if first or last tab is scrolled off it won't come back by arrows or scrolling.
Scroll wheel: With mouse cursor in the tab line, turning the scroll wheel away moves a white highlight leftward through the tabs, and the corresponding webpage becomes visible. The first tab remains off to the left and not visible. One click after the 2nd tab is highlighted, the highlight disappears but the 1st webpage becomes visible. Thus, the scroll wheel is able to select any page, but the tabs for the first and last pages don't become visible. No difference noted between scrolling at left or right end or with tabs on top or not on top.
(Recall that when the problem occurs, clicking the left or right facing triangles at the ends of the tab line doesn't provide access to the first or last webpages, so the scroll wheel behavior is slightly better than the triangle behavior. Also, the first and last webpages can be selected ok via the dropdown list selected by the down triangle at the right end of the tab line, but again the first and last tabs remain off screen even though their webpages are selected and visible.)
browser.tabs.onTop setting: The problem symptoms appear to be the same for both the True and False settings of browser.tabs.onTop. When the setting is changed, the tab line moves to its alternate position, first or last among three toolbars. If the first or last page is selected when the setting is toggled, the tab line that appears has the corresponding tab visible and it stays visible as setting is toggled. But if the tab line is then scrolled such that the first or last tab scrolls off, the first or last tab won't scroll back into view, ie problem remains.
I will wait until about 0700 UTC on 5 Jan before restarting FF in case there are any other tests to run or information needed from files in /proc/6626, and then will restart in safe mode and run it that way until problem recurs or until I restart for some other reason.
Try to create a new profile as a test to check if your current profile is causing the problems.
See "Creating a profile":
If the new profile works then you can transfer some files from an existing profile to the new profile, but be careful not to copy corrupted files.