Hopefully you have an xpi file. Here is an article that covers how to install using that file:

https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

I do have an xpi file, but the installation instructions you sent don't work because I get an error message saying that the file couldn't be installed because it could not be verified (even though I got the file from the official TB website for add ons. The file is named: "MorefunctionsforAB-TB3-1.0b.xpi. Curiously, when I download it from my Firefox download manager, the name changes to: morefunctionsforAB-TB3-1.0b3, so I don't know if that is a download malfunction, or a normal process. If I can't install this file, then I can't recover my address book contacts. Please help if you can. Thanks. Rainer

Is there another add on or another way to recover my address book contacts? Is it possible to use Windows "system restore" to recover the contacts? Thanks. Best, Rainer

That sounds like you were trying to install it into Firefox.

Just open your Tools|Add-ons window in Thunderbird, then drag and drop your xpi file onto it.

When I click on tools in thunderbird, there is no add on option. There is an add on as a separate tab, but that seems to take me to firefox. Is there another item in the tools section I need to click to get to the tools add ons? Like "import"? Let me know. The only things on the tools menu are: Address Book Saved Files Chat Status Join Chat Run Junk Mail controls Delete Junk Mail Import Developer Tools Clear Recent History That's it. There is no Add Ons in the Tools section. The Add On stand alone tab takes me to Firefox every time. What am I doing wrong? Thanks for your help

Tools|Add-ons refers to the traditional menu across the top.

If you use the newer "Application Menu" (the doohickey with three bars, looks a bit like a hamburger in a bun) the Add-ons item is at the top level.

I'm using Linux and I have my buttons in non-standard places, so don't expect to see exactly the same in yours.

This article can be helpful: http://kb.mozillazine.org/Menu_differences_in_Windows,_Linux,_and_Mac

Hi Zenos, OK, I'm sending you a screen shot of my TB add ons screen. Where do I drag and drop my add on in this screen. I looked over your suggested website, but didn't find the help I need. I appreciate your efforts and all who contribute their time and energy to Thunderbird users, but I'm getting nowhere fast. Please look at the screen shot and guide me from there. Thanks ever so much.

Best, Rainer

Try the dark bar at the left.

Ironically, the "Get Add-ons" tab is the least helpful. Switch to the "Extensions" tab and you can drop most anywhere. The "Extensions" tab also has a button with an "install add-on from file" option.

The "Get Add-ons" tab is a serious waste of space and users' time. :-(

It's sad that Thunderbird doesn't appear to have a formal style sheet or design guide, and their designers occasionally go off the rails. Three more of my pet hates:

1. "Account Actions" button changes its label;
2. "New Message" does a whole lot more than start a new message;
3. "Add Contact" drop-down zooms out at me, making me flinch, every single time.