How the heck do you drag a picture in gmail?

For many years I used an old version of Thunderbird (3,x) for my gmail.
All of a sudden google decided my thunderbird was too old and not
secure. Yet it worked fine and I could give a rats ass about security,
especially when my emails are very6 boring for anyone who would attempt
to read them, while most of the world posts their who life on Facebork
and the whole world can read it.

Anyhow, I was forced to upgrade Thunderbird to the latest ver that XP
allows. For some reason, I can READ my email, but can not post from it
on TB. I;ve entered my username and password till I turned green and it
still wont work.

So, I am forced to do my gmail on the web, and I hate the format they
have. Anyhow, in TB if I wanted to upload a picture, I'd go to the
folder where I have it and click on the filename. On web based gmail, I
must DRAG the photo to the page. NOT BOTH at the same time. This is a
laptop with a 13" screen. I'd need a giant monitor to load both at the
same time.......