Reproducable with uGet and Free Download Manager, both macOS and Linux.

Tested the issue on chrome reported version 69.0.3452.0 using Ubuntu 14.04 and Mac 10.12.6 with steps mentioned below:
1) Launch chrome reported version and installed uGet and Free Download Manager extensions from Webstore
2) Navigated to https://speed.hetzner.de/ and downloaded the file, able to see file download in download bar at bottom of the page

@Reporter: Please find the attached screencast for your reference and let us know if we missed anything in reproducing the issue, provide your feedback on it which help in further triaging it in better way.

Thanks!

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You didn't get it. Chrome shouldn't download the file, it needs to be intercepted by extension and downloaded by custom app. 

BTW for full test you also need to install uGet on machine and you will see that file is downloaded twice: by chrome and uGet.

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Tested the issue on chrome reported version 69.0.3452.0 using Ubuntu 14.04 with steps mentioned below:
1) Launch chrome reported version and installed uGet on my machine(as mentioned in comment# 4) and install the uget integration extensions from Web store
2) Navigated to https://speed.hetzner.de/ and downloaded the file, able to see file download in download bar of chrome browser

@Reporter: Please find the attached screencast for your reference, if possible could you please provide the steps how to integrate Uget app on machine with the Uget integration extension and please provide screencast of the issue which help in better understanding.

Thanks!

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You also need to install uget-integrator: https://github.com/ugetdm/uget-integrator/wiki/Installation#ubuntu--linux-mint

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

As Uget is already installed in my local machine, as per comment# 7, navigated to URL: https://github.com/ugetdm/uget-integrator/wiki/Installation#ubuntu--linux-mint and tried installing Uget integrator through terminal using "sudo apt install uget-integrator", getting the message as "Unable to locate package uget-integrator".
@Reporter: Please find the attached screencast for your reference, could you please provide steps to install the Uget-integrator which helps in further triaging it and if possible provide screencast of the issue which help in better understanding.

Thanks!

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You need to add corresponding PPA as in instructions.

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Unable to reproduce the issue on chrome reported version 69.0.3452.0 using Ubuntu 14.04 and 17.10, please find the attached screencast for your reference. As per comment# 0 from the reporter as this issue is seen on Arch Rolling, ET team doesn't have Arch Rolling to test and confirm the issue, hence routing this issue to Inhouse team for further triaging the issue and adding TE-NeedsTriageFromHYD label.

Thanks!

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Unable to reproduce the issue on debian rodete with chrome #69.0.3452.0 as per steps mentioned in comment #0 and observed that files are downloading in uget application

Since TE doesn't able to repro this issue adding TE-NeedsTriageHelp label for further triage. Requesting Extensions dev team to look into this issue.

I can't no longer reproduce it on macOS/69.0.3472.3 with Free Download Manager. 
I will try at home with Linux.

Still reproducable, even on Windows. Please try Windows/macOS with Free Download Manager.