Could you check the Add-ons page? Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then see whether you can find Yahoo on the right. Disabled extensions cluster toward the bottom below the enabled extensions.

Does it mention any reason for being disabled? I have a guess...

Firefox 43 now requires that extensions be digitally signed by Mozilla. This article has more information: Add-on signing in Firefox.

Unfortunately, Yahoo hasn't yet updated for this.

You can get a signed version from the Mozilla Add-ons site: https://addons.mozilla.org/firefox/addon/yahoo-toolbar/

[OLD COMMENT] You can make a temporary exception to the signing requirement -- this is global for all extensions, there's currently no way to only make an exception for one specific extension.

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

(2) In the search box above the list, type or paste xpin and pause while the list is filtered

(3) Double-click the xpinstall.signatures.required preference to switch it from true to false -- note that this is for Firefox 43 only

Hopefully Yahoo will get its act together soon! (Sorry Yahoo, but why don't you redirect your Toolbar page to Mozilla Add-ons?!)

Scratch that, Yahoo now has uploaded the latest version to the Mozilla Add-ons site:

https://addons.mozilla.org/firefox/addon/yahoo-toolbar/

Please reinstall from that page.

Thanks for your reply. FYI, I have already tried tools>add-ons, then clicked extensions, which is just a blank page for me, i.e., no Yahoo or Yahoo Toolbar appears anywhere. Also, had already tried the site you have suggested https://addons.mozilla.org/firefox/addon/yahoo-toolbar/ but it doesn't work...see the reviews on that page. It appears everyone is having this problem and this page doesn't fix problem. I haven't yet tried disabling signatures, I will try that and let you know. Thanks. Burt

Disabling signatures didn't work either. Plus, when I restart Firefox the xpinstall.signatures.required preference resets back to true even though I had set it to false before restarting Firefox.

Also, forgot to add, when I download Yahoo Toolbar from the site https://addons.mozilla.org/firefox/addon/yahoo-toolbar/ and it asks me to restart Firefox I get a crash notice when I click on the restart Firefox now button.

Hmm, lots of problems.

First, Firefox should not lose settings changes. However, if Firefox crashed, it's possible that the settings files on disk were not updated.

Does Firefox have problems saving any other settings changes, such as your home page? We have a general support article on that: How to fix preferences that won't save. There also are utility/security programs (such as Advanced SystemCare) and some malware that can roll back settings changes between sessions. I'm not sure the article mentions checking for those.

Second, it is normal to have to restart Firefox before old style extensions are installed/enabled. But of course it's not normal to crash. If that happens again, could you check the support article "Firefox crashes - asking for support" for steps to get the crash report IDs from the about:crashes page, and then post a couple of the recent ones here.

Third, there are times when Firefox's settings files that store extension information become corrupted. If that is contributing to the problem, here's how you can force Firefox to regenerate the files:

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Show Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

Pause while Firefox finishes its cleanup, then rename any of these files that you find:

• compatibility.ini to something like compatibility-old.ini
• extensions.ini to something like extensions-old.ini
• extensions.json to something like extensions-old.json
• extensions.sqlite to something like extensions-old.sqlite (might not exist depending on how long you've been using this settings folder)

When you start Firefox back up again, it should explore your profile folder, other folders, and the Windows registry to rebuild the list. It probably will ask you to approve some of the extensions. Once things settle down, any improvement with the Yahoo toolbar?

This is the download link for the crash report, can you access this? https://crash-stats.mozilla.com/report/index/85cdd31f-807c-4ee7-98a8-dbbb42151218

OK, not sure what I did, but I got Yahoo Toolbar loaded onto Firefox; had to re-customize buttons as it wasn't my customized Yahoo toolbar. But in about:config none of my changes were being saved. So went to menu:help(?):troubleshooting information and then "show folder" for profile folders. Had over five thousand numbered profile files with zero bytes...deleted them all, still didn't save config changes. Then deleted the unnumbered profile file and restarted Firefox. Presume a "clean" version of the unnumbered profile file returned, made your change to config file for xpinstall.signatures.required to false, then edited profile file where I saw a line that said yahoo.toolbar.upgrade, false, I deleted that line. Restarted Firefox and everything worked and all config changes were saved. Thanks Burt

Thanks for the report back, and your persistence. I don't know why the prefs.js file sometimes becomes locked and un-updateable, but it sounds like that was the main problem.