If someone shitted on your Firefox settings, for example your organization. Maybe they forced some configurations, for example, opening new links into new windows.
If you, like me, hate window spreading chaos, you probably want to manage every tab inside only one Firefox Window.
There are three about:config settings to check:
browser.link.open_newwindow.override.external = 3- -1: Use default behavior (follow browser.link.open_newwindow)
- 1: Open in the current tab (replace it)