Add instructions for some Android browsers and update Firefox desktop instruction.

[mjholub]

Could also be moved to the bottom with separate headers for mobile and desktop browsers. Of course the extensions needs to eventually be packaged and published in the Firefox Android Store. Tested with Firefox Nightly. The disclaimmer in the instruction for desktop now reflects the extension being available in the Firefox Store.

[asieduernest12]

@154pinkchairs i meant to recommend you include those changes as a new commit where you specify step that will let anyone use the codes you provide and then you include an extra step or a link on how to make their own collection. Many people are security conscious so it helps them know that they can make their own collection. then i can merge this if all looks good.