Unfortunately, it’s not compatible with 2.6. You’ll need to update to the Endless OS 3 series in order to get app updates and continued support. Do you need help doing this? This is the post on how to do it:
community.endlessm.com
Upgrade from Endless OS 2.x to Endless OS 3
Upgrade from Endless OS 2.x to Endless OS 3 Limitation: This FAQ applies to Endless users with version 2.x only. To upgrade to Endless OS 3, follow these steps: Update to the latest 2.x version. You can do this by going to Settings > Details > Ch…
After you upgrade to the latest version of Endless OS, you’ll see Firefox, Chrome, and other apps ready to download with one click in the App Center.
Hope this helps!