When you open a link from an external program, go to the about:profiles page in Firefox. You will probably see multiple profiles listed. Press the Set as default button next to your regular profile. The next time you open a link in another program, it should open on the regular profile and hopefully in a new tab.

Hope this helps.

This works but with previous firefox versions i didn't have to setup default profile.

You can't specify a profile when you open an external link, so you can only make this work if the profile you want to use is set as Default=1 in profiles.ini or selected in the Profile Manager. If no profile is present in the Password Manager then a new default-release profile will be created.

Some people had this problem due to a recent change to how Firefox handles profiles. The goal was to allow users with more than one Firefox installed (for example, Firefox and Firefox Beta) to run on separate default profiles.

Unfortunately, for many users, Firefox thinks that open from an external program is an entirely new Firefox version, so it ended up creating a new profile and setting it as the default.

With the steps I listed above, that should be fix it permanently for you.

If you have never used the Profile Manager to create a profile (i.e. not profiles present in profiles.ini apart from a default-release profile created by Firefox), but only use a direct path then that won't work because Firefox won't be able to locate your profile. Only if a profile is listed in the Profile Manager (profiles.ini), you can make external links work properly like I wrote above.