See revised version below

Let me try that again, with more accuracy.

In your system details I notice this setting:

privacy.sanitize.sanitizeOnShutdown: True

This relates to your setting for what history to clear when Firefox closes. When you change this setting, it probably switches your Options > Privacy tab from "Remember history" to "Use custom settings". To edit the setting, look for "Clear history when Firefox closes" on that tab.

I wonder whether those settings are affecting what appears on the Windows 7 Jump List?

But that wouldn't explain why your Tasks section is incomplete... do you have New Window and New Private Window?

Note: The Pinned section doesn't show frequently visited sites. Those should appear under Frequent (see example attached).

I know that the Pinned section doesn't show frequently visited sites...I meant "pinned" in the sense of the Firefox icon that's pinned to my taskbar...sorry I wasn't clearer about that.

I don't have either the "New Window," or "New Private Window." I don't have a "Tasks" section at all.

I'll adjust the setting you mentioned, and see if it changes anything. :)

PS...I just checked the setting in question, and it shows as "false."

You're right, I probably read your post too fast. I rarely use the Jump List feature except to launch a new copy of Paint or Notepad, so I haven't had the occasion to research what can "break" the normal display of the list. Hopefully someone with more experience can chime in.

PS...I just checked the setting in question, and it shows as "false."

Maybe toggle it a couple times, either in about:config or using the dialog. There's something odd going on there.

If you notice specific settings changes not sticking, check out this article for troubleshooting advice: How to fix preferences that won't save.

Well, I've checked the setting, and toggled it a few times, like you suggested, and it seems to stick as "false," but I still don't see anything in the jumplist.

As long as we're turning things off and on again, you could try unpinning and re-pinning Firefox on the task bar, per this thread: No Jumplist options on firefox 10.0.2. Hope that works!

Well, I tried that (unpinning and repinning the icon), but still no websites in the jumplist.

I checked the link you provided, and tried unpinning and re-pinning the icon, as well as checking my Start Menu settings, but still had no luck with websites in the jumplist. Interestingly, if I install Firefox 20, I do get the websites showing in the jumplist, just like they're supposed to, but if I update to version 21 (either manually or automatically), the ability to add new sites into the jump list (if I delete one, for example) is gone.

Could you check some preferences in the about:config preferences editor? I'm not sure why these would have non-default settings, but "stuff happens."

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the filter box, type or paste task and pause while the list is filtered

In particular, check for non default settings with the "lists...enabled" items:

browser.taskbar.lists.enabled default: true
browser.taskbar.lists.frequent.enabled default: true
browser.taskbar.lists.recent.enabled default: false
browser.taskbar.lists.tasks.enabled default: true

Also, in case this somehow got zeroed:

browser.taskbar.lists.maxListItemCount default: 7 (max:10?)

jscher2000,

I checked all the preferences you mentioned, but they're all the same as what you've listed.

I spent another hour researching this and I'm coming up dry. The "Frequent" section of the jump list should match the top sites on the Most Visited list ("Smart Bookmark Folder" with the blue icon). No reason for the Tasks section to be missing. Maybe there is a flaw in the installer? Unnoticed change in the code?? It might be time to file a new bug on this.

Could be. I did get a jumplist rebuilt by installing FF20, building the jump list, and then installing FF21...so FF21 has a jumplist on my install now. But it's still weird.

jscher2000, I've filed a new bug report:

https://bugzilla.mozilla.org/show_bug.cgi?id=874564

Just got an email from Bugzilla...it looks like the bug's already been noticed, and reported.

https://bugzilla.mozilla.org/show_bug.cgi?id=870529

Thanks, meanwhile I was poking around and discovered the file that Firefox creates for the Frequent and Tasks sections in this folder:

%APPDATA%\Microsoft\Windows\Recent\CustomDestinations

On my system, the file is named 969252ce11249fdd.customDestinations-ms but I have no idea whether that is static or dynamically generated by Windows/Firefox.

Renaming that file immediately hid the upper sections of the jump list. Restarting, browsing, exiting, and restarting Firefox 21 did not create a new file, but I only gave it a few minutes before undoing the change.

So... I didn't lose my Firefox 20 jump list but Firefox 21 might be having issues creating it in the first place.

Well, I looked for that file, but I couldn't find it...and the image you attached is exactly what my Firefox 21 icon looked like, before I reinstalled Firefox 20, rebuilt my jump list, then installed FF21.