Wenn ich zu viele Tabs offen lasse, brauche ich länger, bis ich den richtigen Download finde.

Because the sentence begins with a subordinate clause: Wenn ich zu viele Tabs offen lasse.

In German, when a subordinate clause comes first, the conjugated verb in the main clause must come immediately after it. So the main clause starts like this:

• ..., brauche ich länger ...

This is the normal verb-second pattern in German. The whole wenn-clause takes up the first position, so brauche has to come next.

Compare:

• Ich brauche länger, wenn ich zu viele Tabs offen lasse.
• Wenn ich zu viele Tabs offen lasse, brauche ich länger.

Both are correct.

Because wenn introduces a subordinate clause, and in German subordinate clauses usually send the conjugated verb to the end.

So:

• ich lasse = I leave
• but after wenn: wenn ich ... lasse

That is why you get:

• Wenn ich zu viele Tabs offen lasse

The same thing happens later with bis ich den richtigen Download finde:

• ich finde
• but after bis: bis ich ... finde

Offen lassen is a common expression meaning to leave open.

It is made of:

• offen = open
• lassen = to let / to leave

So:

• Tabs offen lassen = to leave tabs open

This is not a separable verb in the same way as something like aufmachen, but it behaves like a verb phrase with a complement:

• Ich lasse das Fenster offen.
• Ich lasse die Tabs offen.

In your sentence:

• Wenn ich zu viele Tabs offen lasse = if I leave too many tabs open

Zu viele means too many, while viele just means many / a lot of.

So there is an important difference:

• viele Tabs = many tabs
• zu viele Tabs = too many tabs

The sentence is saying that having that number of tabs causes a problem, so zu viele is the natural choice.

In German, länger brauchen is a very common way to say that something takes longer or that you need more time.

So:

• Ich brauche länger. = I need longer / It takes me longer.

German often leaves the comparison implied when it is obvious from context. English does this too sometimes:

• It takes longer.

You do not always need to say than usual or than before.

Here, bis means until.

The structure:

• Ich brauche länger, bis ... means
• It takes me longer until ... or more naturally in English:
• It takes me longer to finally ...
• I need more time before I ...

So the sentence is describing the amount of time that passes before the speaker finds the right download.

Also, because bis introduces a subordinate clause here, the verb finde goes to the end.

Because finden takes a direct object, and that object is in the accusative case.

The noun is:

• der Download in the nominative

In the accusative masculine, der changes to den:

• den Download

And the adjective also gets the matching ending:

• den richtigen Download

So:

• Ich finde den richtigen Download. = I find the right download.

Because in German every noun has a grammatical gender, and Download is masculine:

• der Download

There is not always a logical reason you can predict from English. Loanwords often simply get assigned a gender and that becomes standard usage.

So the forms are:

• nominative: der richtige Download
• accusative: den richtigen Download

Yes. Modern German, especially in tech and internet contexts, uses many English loanwords.

So native speakers often say things like:

• Tabs
• Download
• Browser
• Link
• Datei
• Ordner

Sometimes there is a more traditional German alternative, but the English-based term is still very common. In everyday computer-related German, Tabs and Download sound natural.

Because bis ich den richtigen Download finde is another subordinate clause.

German subordinate clauses usually place the conjugated verb at the end, so:

• main clause: ich finde den richtigen Download
• subordinate clause: bis ich den richtigen Download finde

This is the same rule you saw with wenn earlier in the sentence.

Yes, but the meaning changes slightly.

• Wenn ich zu viele Tabs offen lasse focuses on leaving them open
• Wenn ich zu viele Tabs geöffnet habe focuses more on having too many tabs open as a state/result

Both can work, but offen lassen feels very natural when talking about the habit or action of not closing tabs.

You could also say:

• Wenn ich zu viele Tabs offen habe, ...

That is probably the most everyday alternative for many speakers.

They are similar, but not exactly identical.

• Ich brauche länger focuses on me needing more time.
• Es dauert länger focuses on the process itself taking more time.

In many contexts, both are possible:

• Wenn ich zu viele Tabs offen lasse, brauche ich länger ...
• Wenn ich zu viele Tabs offen lasse, dauert es länger ...

The first sounds a bit more personal; the second sounds a bit more neutral.

Yes. It tells you what takes longer.

The structure is:

• I need longer / it takes me longer
• until I find the right download

So the sentence means that leaving too many tabs open delays the moment when the speaker finally finds the correct file or download link.

It is a very natural way in German to describe how long it takes before something happens.