I am looking for this Firefox extension called FirstField, but for Chrome. Essentially, you press a keyboard shortcut and it focuses the first text input field on the webpage (for example, the Wikipedia search). How difficult would it be to create this?
A quick search for focus on the Chrome Web Store brought up Input Focus. It looks like it will do what you want, press Ctrl+Alt+L to set focus on a page's first text field and then press the combo again to start cycling through whatever other text fields are on the page.
If you're looking for something even more comprehensive, I've been super happy with the Vimium Chrome Extension which is especially fluid if you know a bit of VI(M), but useful even if not.
If you install Vimium, you can snag the first input field by typing
You can then tab to other text entry fields.
Alternatively, you can prefix
As an additional alternative, you can type