Click button in a web page (Firefox)

Questions & Suggestions
1

Hello!

How to click a button on a web page using Firefox, without using mouse clicks or click by image found etc?

Button id: <input id=“fileupload” name=“files”

2

Firefox has no support for AppleScript, so other than UI control you have no options.

3

I haven't tried this, but maybe it will help:
See Inject Javascript in Firefox - Stack Overflow.