~~It works properly for me~~ ~~firefox 79.0~~ ~~archlinux~~

~~proof: https://imgur.com/iJRU5gU~~

Hi DenverCoder9, does it seem to be a new instance of the identical Firefox, or are there differences? I'm asking because this can happen when your first instance of Firefox is not running what is recorded in various config files as your default Firefox profile.

To see which profile each window is using, you can check the Troubleshooting Information page. Either:

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter/Return

In the first table on the page, find the Profile Folder row and check the last part of the path. Same profile? Different?

You might also check the Application Binary to see whether you have two Firefox installs.

Depending on what you find, we'll have different recommendations.

Oh no actually without specifying the website, it opens a new window for me too. The profile folders and the application binaries are the same in both the windows

ie `firefox https://duckduckgo.com --new-tab` opens a new tab in the already running window. `firefox --new-tab` opens a new window

Thanks for the update, Chinmay.

@jscher2000, I just checked: the windows have the same profile directory and also the same application binary. FWIW also, if I just keep running the command, it is always opening a new window, even with the one it just opened still there.

Using -new-tab without a URL following isn't documented currently. Not sure whether it used to be documented:

https://developer.mozilla.org/docs/Mozilla/Command_Line_Options#Browser

You could add a URL to your shortcut (e.g., "about:blank").

Or file a bug if you don't need it for a while: https://bugzilla.mozilla.org/