Hi. I use ESR (78.13) for Linux on two laptops, and the current version for Android (91.3). Sync is enabled on all these devices. I just ran a test: I sent a tab from one laptop to another and back, and it worked immediately. Sending a tab to mobile fails; no notifications, nor errors. However, I can sync tabs accross devices with no problem. I can also send the URL via NPC and Bluetooth, so it is not any of the laptops, nor the device that is failing. I have noticed that on Android, when I start the browser the Sync option is set to "Sign in to sync"; if I tap there, it shows my sync account info; it doesn't ask for my username nor password. Perhaps this is related. Please help! P.S. I looked at this question but it is archived: https://support.mozilla.org/en-US/questions/1284364. I have the exact same issue.