I should add that this has been going on for a while (FF13, FF14 betas), so it's not something new. I was just hopeful that some newer beta might fix this, but since I have this issue now for a long time (can't even remember when it started), I think it's time to find a solution or report a bug.

I've seen this happen myself when no tabs show on the tab bar and new tabs are added to the right of the new tab button that does appear at the far left in this case.

Looks like this bug:

• bug 714382 - Leftmost tab is hidden when reopening browser window

Do you have steps to produce this that works all the time (e.g. in a new profile)?

Then you can try to reopen the bug or file a new bug for the current Firefox release (the bug was for Firefox 10)

The thing is, there are a few bug reports that seem to describe the same/similar issue:

• https://bugzilla.mozilla.org/show_bug.cgi?id=666822
• https://bugzilla.mozilla.org/show_bug.cgi?id=696684

plus the one you mentioned:

• https://bugzilla.mozilla.org/show_bug.cgi?id=714382

But since the report that most exactly describes the problem is listed as "resolved" and I have the issue in the latest FF14 beta, I figured, I create a new bug report:

• https://bugzilla.mozilla.org/show_bug.cgi?id=774943

Obviously something's going on, and has been for a long time, but it seems to affect only few enough that it never gets fixed.

With the latest Firefox 15 beta 1 this behavior seems to have gone away.

At least after upgrading on one computer, the same session that used to be restored corrupted was restored properly. No safemode or anything like that, just regular auto-upgrade.

Of course, this doesn't mean this behavior may not be back at some point in the future, but it means something relevant was changed in that the same session was loaded properly now.

Same add-ins, extensions, etc. too.

Let's hope this is the last word on this.

There's still one minor issue: the first/active tab, while being restored, doesn't show the URL in the URL field unless one first switches to another tab, and then back. Before that switcheroo, it just shows an empty field with the "Go to a website" legend. Adding and then deleting a tab (if it's the only tab), or switching to another tab, and then back to the first one, will display the correct URL. This however is minor, and it doesn't affect usability in a significant way.

I've been having this issue since firefox 12. I'm tired of my the leftmost tab disappearing every-time I reopen the browser. To try to get back that missing tab, I have to scroll from the last tab on the right, then make the hidden tab the active window, detach the tab (thanks to duplicate tab add-on) from that window, then re-merge the separate window back as a tab on the original group. It gets tedious since I save 4 or more windows with multiple tabs on them. I was considering changing browsers but I have too much history, tabs etc that I want to keep. If this continues I will have to switch though.

P.S. Why was the dropdown arrow at the end of the tab row removed? That way I can just select what tab I want to make active even if it was 'hidden' You guys need stop removing useful features with all these new updates.

Just wanted to chime in to say I've been having exactly this issue as well for a long time. Can't remember exactly when I first noticed it, but it was definitely several versions ago (12 or earlier). With each new version I hoped to see it fixed, only to be let down. I'm currently running FF 14.0.1 on Win 7 (64-bit) with only a YouTube downloader add-on btw.

I haven't analyzed the behavior in much detail since it's just a minor nuisance, but the pattern is non-trivial as far as I can tell. Most of the time I can restore multiple tab-filled windows with no trouble, but once in awhile one of them will have the new tab button on the left side with the first tab hidden and inaccessible upon restore. I don't think I've ever seen both windows exhibit the problem at the same time however. Once the problem starts, the affected window is subsequently messed up on every restore. I haven't been able to find any way to restore the default look/behavior short of closing the affected window and creating a new one.

Hopefully this will be fixed now that the OP filed a new bug report.

Is this a problem with the sessionstore.js file or with the localstore.rdf file as those are the most obvious to me in this case?

• http://kb.mozillazine.org/sessionstore.js
• http://kb.mozillazine.org/localstore.rdf

Is this behavior repeated if you close and reopen Firefox?

Not sure which it is, there are however two more minor observations:

a) with the latest betas of FF15, this happens less often b) when FF crashes and then restores the windows, it hardly ever happens, OTOH, when I quit FF and then restore a session when I relaunch FF, it happens rather often c) in some cases, this even happens if I drag a tab out of a window such as to open it in a separate window, which makes me wonder if it's something that has to do with some sort of page properties or JavaScript, because if I simply create a new window, this never happens.

As rcfa mentioned, creating a new window manually never causes it; only session restores.

After doing a little more digging though, I found the culprit to be the DivX HTML5 Web Player extension, at least in my case. Disabling this extension and restarting FF causes everything to go back to normal! Re-enable it and the problem returns. I repeated this a few times to verify the correlation.

I wouldn't have guessed that type of extension could cause such weird layout issues, but I'm glad to finally have a solution. Not sure if this solution applies to the OP (though the problem description is identical), but hopefully this can help some others.

That solved my problem as well. The DivX HTML5 Web Player extension was definitely the culprit. I'm uncertain why this would cause the problem but, Mozilla please get on DivX case and get them fix the add-on coding to work properly with firefox!

Thanks for your help everyone