The documentation is unfortunately slightly incorrect. In TB, click the AppMenu button (3 horiz. bars) then Options...Options, or from the Menu Bar select Tools/Options(Mac:Preferences). Next, click the Attachments tab, Outgoing, click the Add button, then 'Select an online storage service'.

The rest of the documentation appears to be correct for TB.

Thank you for your quick response. However, I don't see 3 horizontal bars in Firefox or Thunderbird. Where are they, or how do I get them to appear?

It's a button that is supposed to replace the Menu Bar, and has been around since Nov. 2012, so it may not appear if you're using an older version. Press Alt if the Menu Bar is hidden. http://mzl.la/MMZqU3

I have the current version of Firefox. The Menu bar is showing, but no 3 horizontal lines. When I hide the Menu bar a Firefox button appears in the upper left corner. Clicking on this presents a menu with an Options options, but no Attachments option within this (as the Filelink instructions say). Still no 3 horizontal lines including when I press ALT. Another suggestion?

You have to set up Filelink in Thunderbird, not Firefox.

This help forum is for Thunderbird. Since you keep saying Firefox maybe you need to go here. https://support.mozilla.org/en-US/questions/firefox

sfhowes has said repeatedly Thunderbird. If you want to follow his instructions, use the right software or go to the other forum for Firefox help.

Hold on. I found the Attachments in TB. I'll post again if I have more problems.

And I corrected the template reference in the article, but the template needs more work.

Thanks for your help. I got it to work, but not in the way described in the instructions. I created an account with Box and uploaded my attachment. The instructions say a link appears where attachment appears. The recipient clicks on the link and what I'd uploaded will be downloaded. Instead I had to get the link from Box and place this link in the body of my email. I don't know yet if it'll work on the receiving end.

that is not really getting it to work. I can do that without any Thunderbird filelink.

What happens when you attach a suitably large file to a Thunderbird message?

A Box account has been set up and my 50MB file has been uploaded. In my email I attach the 50MB file which resides on my computer. A message at the bottom of the email asks if I want to use Filelink. Click on Link. Window opens, I select Box and click "Get a Box account." I'm taken to the Box website where I sign in. My uploaded file is there. Right click on the file > Share > Get Link > A window opens with the link to be copy/pasted. This is what I used to get the link into my email. There's another option in this window: "Direct Link." Clicking on this opens a window which says "A direct link allows users to avoid the download page and opens the file immediately." This may or may not allow the recipient to directly open the attachment (which would actually be the link to the 50MB file on Box). But this requires a paid upgrade. Any thoughts?

Nope that is working correctly. I was obviously wrong last time.

Direct links can be good for images, but if your sending someone a video or a large cad file it would be the last straw in frustrating if the file tried to open in the application from a direct link.