Custom Links in Lightning Experience open in a new web tab instead of a new window

Salesforce Custom Links use standard HTML link targeting (target='_blank') to open content in a new browser context. Whether this opens a new tab or a new window is determined by the browser, not by Salesforce. The steps below describe how to change this behavior in common browsers

Web browsers may opt to open links in new web tabs instead of new windows even though they are configured to open in a new window.

• To prevent this behavior in Firefox, disable "Open links in tabs instead of new windows" from your Firefox settings/preferences.
• To prevent the behavior in Chrome consider installing an extension to force pages to open in new Windows instead of tabs.