I think not only app but from the very first firefox addon would be great too but I have different version. I think it will be very hard to push website owners to accept your btc tip method but as I see a lot of them have paypal donation buttons. With addon, it will be grest if users are able to pay 1$ or any amount with bitcoin and then you automatically donate it in usd but now as I realize my idea is hard and probably worse because of paypal tos. But addon would be great.
That would be very hard and legally tricky.
True. You probably can't just jump onto something like building (so hard and) secure Firefox or Chrome addons directly without any funding. Start with what you're thinking to build (talking about the protocol, the easy part). Once you're ready with it, keep improving it with the funding you receive in the shape of little commissions. Ultimately, you'll be able to build such add-ons for the protocol with the funding of total commissions.
Literally, "a lot of" crypto startups have become successful by following this path (starting with nothing, becoming everything). "Blockfolio" (mobile application) is an example of such success. IMO, crypto-industry is still lacking basic stuff, and start-ups (like the one you're planning) have so much potential!
bitcoin is not good for tipping -- fees eats up most of it. You thought of any measure to prevent this?
Maybe you should consider reading the first few posts of this thread?