Hah!

I trashed my entire Firefox installation and launched v 67.0, and only then did I see the screen you're referencing. I clicked on "Skip this step," and was then in the same situation you're in. (I hope I can reproduce my original situation from my clone.)

I'm guessing here, but it looks like you somehow got into a "new installation" situation rather than having v 67.0 overwrite and perpetuate your present installation.

You may need to contact Mozilla.

For what it's worth, my update procedure, done while I"m on line, is:
  1. Copy new version from .dmg.
  2. Paste it over my existing earlier version (which is stored in my data partition).
  3. Launch new version.
  4. Click to OK download.
and that procedure perpetuated my prefs, etc.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire