Right now, we can only open individual tabs from others. If I want to open all the tabs from my smartphone on my laptop, it's not doable. Following options will be very much convenient if it would be added.
For all the new posts about opening hundreds of tabs on firefox android app :
The original question was about opening all tabs from any device on firefox desktop browser and the solution is here.
For those who need to open all tabs from a device on firefox for android, the solution is quiet simple, don't try to do it from de mobile, just send them from firefox desktop.
On Firefox desktop :
1) Right clic on any tab,
2) clic on "Select all tabs",
3) right clic on the selected tabs,
4) clic on "Send xx tabs to a mobile",
5) choose the right mobile in the sync devices list.
Done, you'll have you're xx tabs opening in the device.
==>For those who need to transfer all tabs from a mobile to a another mobile, just use firefox desktop between them, using the first solution then this one.
==>And for those who have the sending tab through mobile broken (my case on a Fenix Beta) you can bypass the issue using Bookmarks syncing.
1) Just select all your tabs like describe above,
2) right clic on it and select "Bookmark those tabs",
3) choose the name and location of the folder where the bookmarks will be saved,
4) go to your firefox for android, make sure you have selected bookmarks in your sync/Account parameter,
5) while you're about it use the "sync now" option,
6) find the folder in your mobile bookmarks,
7) clic on the 3 dots on the right,
8 ) choose "Open all in new tabs".
You'll have all your tabs opening in your firefox mobile in 30 sec steps.