The page to connect another device is merely a page to send a link to install Firefox on that device via a telephone number (only in the same country as your IP locates you, you can't specify the country code). The Firefox Account toolbar button on the Navigation Toolbar has a menu item to send the current tab to a device and menu item to connect another device. If Send Tab to Device" is grayed then this either means that you aren't connected to Sync or that no other devices are connected to this Sync account. In that case you can try to disconnect and reconnect Sync or check the status in "Options/Preferences -> Sync".

disconnect， reconnect operation is expensive。No one want do it with the risk of losing bookmarks, which actually not。

while "Send Tab to Device" is not immediate。

There are two items make me confuse about sync & Connect Another devise:

1. i read some help sync ：https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer when i run Second: step sub 3 item. the connection Another Devise is really make me confuse, without an telephone number input & tell me this just a download page.

2. i also read other pages, that said, firefox will not store bookmarks in self server. So i need to connect my device, Does it older page?. So i guess, it use some tech to connect device together and send bookmarks etc.

Sync lets access open tabs across your desktop, laptop and mobile devices that use Firefox. Your Synced Tabs are just a click away in the Library button on your toolbar. Before you begin, set up Sync on all devices that use Firefox

First and foremost, you'll need to be using the latest release of Firefox for desktop and either Android or iOS. You'll also need to have a Firefox Account. The account is free and enables you to sync history, bookmarks, and more between Firefox browsers. Once you've signed up for an account, you'll need to log into that account on all Firefox browsers that will take advantage of this feature.

Logging in

Logging into your Firefox account is simple. On the desktop iteration, click on the menu button (three horizontal lines in the upper right corner), and click Sign in to Sync (Figure A).

In the resulting window, click Sign In and then enter your Firefox Account credentials. You will then be able to configure what Firefox syncs across your browsers (Figure B).

On the mobile version, click the menu button then click the Sign in entry. Type your Firefox Account credentials, click the Sign in button, and you're good to go.

Send tabs from desktop to mobile

The one caveat to this feature is that it only works from the Desktop; you cannot send a tab from the mobile Firefox to your desktop browser. With that said, to send a tab from your desktop Firefox to any other browser connected to your Firefox Account, do the following:

   1.Open up a new tab
   2.Go to the site in question
   3.Click the three dots at the right edge of the address bar
   4.From the drop-down, click Send Tab to Device
   5.Click on the target device from the list (Figure C)

Very shortly after sending the tab, you will see a notification appear on your mobile device. Tap that notification to open the new tab. Keep the reading or work going from desktop to mobile, it's that easy. Firefox makes the case

With the massive improvements under the hood, little features like this help to make a seriously solid case for Firefox as your default browser. With the release of Quantum, I have migrated from Chrome to Firefox and can't see myself looking back. The ability to easily send tabs from the desktop to mobile makes this choice even easier.

Also see

   ~Mozilla launches Firefox Quantum, its fastest browser ever (TechRepublic)
   ~How to gain quick access to Firefox's forget feature (TechRepublic)
   ~How to force Firefox to forget your browser history (TechRepublic Video)
   ~Why Firefox Quantum could take Chrome's position as the king of browsers (TechRepublic)
   ~How to tweak the new Firefox 57 Quantum browser to suit your preferences (ZDNet)