Assuming that the web browser is compatible with modern web standards...

1. Get an account with a web-based electronic stock trading platform, for example, E*Trade or TD Ameritrade.




2. Use your 5 seconds insight to buy low and sell high.




3. Enjoy your filthy lucre.

Crack any password, ever. Any problem (and there are a LOT) that is hard to solve but easy to verify, and be solved instantly by being able to look into the future.

For a simple example: cracking a combination padlock.

1. Create a simple website, with a form, where you type in a number, click submit, and it displays it back to you.




2. Make a plan: You will open that page. If it is blank, type 0001 and submit.
   If it shows a number, try the padlock; if it opens, type that number in and submit. If the padlock doesn't open, add 1 to the number, and submit it.




3. The only stable outcome is, that the browser view from 5 seconds in the future, will show you the correct combination!

There are a HUGE number of extremely important questions in cryptography, physics, biology, etc etc. that can be checked in a few seconds, but would take centuries to try every possible combination. We're talking world changing stuff here, depending on the intelligence of the team you have working on it... you could do practically anything.

But, you just want money. So, here's what you do: Open a bank account somewhere secure (swiss? caymans? do a bit of research, first). Then go to the online banking portals of other banks. Use your magic password cracking password to open the account of Warren Buffet / Bill Gates / Donald Trump / etc. Transfer their money to you. You are now rich! Just make sure you get all of it - don't want them coming after you! ;)

Get an augmented reality headset, and install a custom firmware on it, which contains the browser open to a page that shows the incoming feed from the camera on the headset. Project this image in front of one (or both, as a sort of overlay) of your eyes.

You now have the ability to constantly see 5 seconds in the future. You can call every coin flip. Tell what people are going to do before they do it. You have inhuman reflexes; you can dodge bullets! Maybe you should become a superhero?

But, the question is how to make money, which is not difficult: Walk into a casino, and start playing baccarat. Or blackjack. Or even the slot machines - some of them use the player pressing a button as the random input to determine the prize, and your glasses let you see exactly when to push it.

You know what every die will roll before it hits the table, shouldn't be hard to make a buck or two from that!

Just sell it.

In speed trading seconds are highly valuable. To a company engaged in that the fair market value of your browser would have to be tens if not hundreds of millions. Full five minutes of advance time on competition would be pretty much license to print money. You would have to figure out a way to filter out the effects of your own trades on the accuracy of the prediction but those guys could pull it off.

You say too much quickly "Poker and similar gives you an obvious advantage but only 5 seconds doesn't grant you the victory."

I suggest to play specifically Omaha's variety and not Texas Holdem, acting in the lapse between you know the cards the crupier shows and your time to play.

How the game works?

You receive your cards. Then there are four streets to bet:

1. Preflop: No cards at the table. You only bet with your cards.


2. Flop: The crupier shows three cards and there is a new bet.


3. Turn: The crupier shows the fourth card and there is a new bet.


4. River: The crupier shows the fifth card and ther is the final bet.

Why Omaha's variety?

At texas holdem you receive two cards. At omaha four. Common best hands on TH are a top pair, while at omaha you frequently have as best hand the nut (the best posible hand on table). So at TH you may fall beting in flop street while turn or river card make you loose the money.

How to profit it?

You need to play at high tables with position. That means you are the last player on the hand playing, to know crupier's cards. Then you just need to bet when you flop the nut or a good flop (note the nut means you win for sure). This is specially important at first street as at Omaha you can frequently flop the nut, but it would be valid also for further streets.
So you will allways play cards that flop a good hand and also bet on turn (where money use also to flow in this variety).

Paradox

The paradox is the server would show your past bets, and so it should be a bit magic showing two paralel time lines and not only the main one where it knows your bet (knowing yourself crupier's cards).

Scalping

Ticket scalping is the process of buying additional tickets to resell at a profit for events. Most of these events use a platform like Ticketmaster.com and the sale only starts on a specific day and time.

Using your browser you can go to the release of a highly desired event and purchase a number of valuable tickets. Since these high profile shows sell out within days if not hours your 5 second lead time should help purchase the tickets before legitimate users. Afterwards you can resell on things like Facebook market place.

ebay

You can start ebay reselling. It is easy enough to discover the true value of a product with some googling. Make a list of the really good deals and then shortly after a product closes bidding you have 5 seconds to place the lowest possible winning bid.

After the purchase you put it back up on the internet with a better value so you can profit from the difference.

Does the browser have magic prophecy powers, or just your specific installation? Because the first would mean that it's unique, and others have given pretty good answers about how you could use that.

If you can just download it to any and as many machines as you want, you end up in a vastly different universe, and I'd like to go open up that angle a bit, because I think you need to either consider this or come up with a very good reason as to why it's not used by everyone. This thing will spread, because it's far too useful, too interesting, and too good of an opportunity to make money for it to stay secret for very long.

In that scenario, it's only a matter of time until many, most, and all other people use it and have the same advantage, resulting in nobody having a real advantage anymore, but being forced to use this browser. Race betting etc. would break down, because nobody would offer these bets if they know that betters know the winner. In stock trading, you'd end up in a similar state to reality, where people fight about microseconds again after everyone has that 5 second advantage.

I'd go so far as to say that in this scenario, you actually could not make much money with this, unless you are one of the early adopters, or you get very, very creative. I could imagine scammers using this in some convoluted "bet on a coin toss while secretly glancing at the browser that shows me a webcam image of the result" scheme, but other than that there's not much room for getting rich quick. Except for one: you have control over the browser's functionality somehow, and can charge people for using it - provided nobody can reverse engineer it and create an open source version or something.

If you just want to have fun and make some (but not shittons) of money, play online multiplayer video game competition. 5 seconds will guarantee you can eliminate any and all opponents with ease.