In de browser kun je snel zien welk tabblad nog open is, want daarop staat de naam van de website.

Because the sentence begins with In de browser, not with the subject.

Dutch main clauses normally follow the verb-second rule: the finite verb comes in the second position. If you put another element first, the subject usually comes after the verb.

• Je kunt snel zien ... = You can quickly see ...
• In de browser kun je snel zien ... = In the browser, you can quickly see ...

So kun je is the normal inverted order after a fronted phrase.

Because tabblad is a het-word: het tabblad.

For singular nouns:

• welk is used with het-words
• welke is used with de-words

So:

• welk tabblad
• welke browser would be wrong here, because browser is a de-word

Also note:

• plural always uses welke
• example: welke tabbladen

Because this is a subordinate clause / embedded question after zien.

The part welk tabblad nog open is means something like which tab is still open. In Dutch embedded clauses, the finite verb often goes to the end.

Compare:

• direct question: Welk tabblad is nog open?
• embedded question: Je ziet welk tabblad nog open is.

That final is is very normal Dutch word order.

Here nog means still.

So nog open = still open.

It suggests that the tab remains open, perhaps while others may already be closed. Dutch nog is very common and often corresponds to English still, yet, or another, depending on context.

In this sentence, the best match is still.

Daarop means on it or on that.

It is a pronominal adverb:

• daar = there / that
• op = on

Together: daarop = on it

Dutch often uses these er-/daar-/hier- + preposition forms when referring to things:

• eraan = attached to it
• erin = in it
• erop / daarop = on it

Here daarop refers to that tab: the website’s name is shown on it.

Yes, staan literally means to stand, but Dutch uses it much more widely than English.

It is very common for text, labels, images, or information that appears somewhere:

• Op het bord staat de datum. = The date is written on the board.
• Op de website staat mijn adres. = My address is on the website.
• Daarop staat de naam van de website. = The name of the website is on it.

So here staat does not mean the name is physically standing up. It means it is displayed, written, or shown there.

Want means because, but it introduces a new main clause, not a subordinate clause.

That is why the word order after want stays like a normal main clause:

• ..., want daarop staat de naam van de website.

If you used omdat, the verb would normally go to the end:

• ..., omdat daarop de naam van de website staat.

Both can express reason, but they are not identical in structure:

• want = coordinating conjunction
• omdat = subordinating conjunction

In everyday Dutch, want often sounds a bit like adding an explanation: because after all / because you see ...

Literally it means the name of the website.

Dutch often uses van for this kind of relationship, especially with things:

• de kleur van de auto = the color of the car
• de naam van de website = the name of the website

English sometimes prefers an apostrophe or a noun modifier, but Dutch very often uses van instead.

Because Dutch nouns have grammatical gender/classes, and each noun takes either de or het in the singular.

• de browser
• het tabblad

There is not always a simple logic you can see from the meaning, so learners often have to memorize the article with the noun.

This matters because it affects other words too, such as:

• welk tabblad (because tabblad is a het-word)
• deze browser but dit tabblad

Here je is most likely generic: it means you in the sense of any user / people in general.

So the sentence is not necessarily talking to one specific person only. It is more like English:

• In a browser, you can quickly see ...
• or You can quickly tell ...

Dutch uses je very often this way in explanations and instructions.

Yes. In nog open is, open is an adjective meaning open.

The structure is:

• tabblad = noun
• open = adjective describing it
• is = form of zijn

So:

• het tabblad is open = the tab is open
• welk tabblad nog open is = which tab is still open

This is similar to English is open, not a separate verb meaning to open.