[M T]

I'm unable to figure out how to  add an attachment.  I'm trying to add a file named IMG_4188a.jpg of size 671KB.

I click Browse and choose a file (its name  is shown).  (If I Post Reply now, it isn't attached.)
I click Add Atachment, and the filename goes away, but I see nothing added. (If I Post Reply now, it isn't attached.)
I click Browse and choose a file (its name  is shown).  (If I Post Reply now, it isn't attached.)
[If I click on Preview Post, the filename goes away.)

What am I doing wrong?  (OSX, both Firefox  &  Safari)

UPDATE: Now answered below.

[M T]

I'm unable to figure out how to  add an attachment.  I'm trying to add a file named IMG_4188a.jpg of size 671KB.

I click Browse and choose a file (its name  is shown).  (If I Post Reply now, it isn't attached.)
I click Add Atachment, and the filename goes away, but I see nothing added. (If I Post Reply now, it isn't attached.)
I click Browse and choose a file (its name  is shown).  (If I Post Reply now, it isn't attached.)
[If I click on Preview Post, the filename goes away.)

What am I doing wrong?  (OSX, both Firefox  &  Safari)

UPDATE: Now answered below.