Install OneTab extension (free) on both machines/browsers. Export from one. Cntl-C to copy the exported text (the urls of all your tabs), then on the target machine/browser use OneTab import, cntl-V to paste the urls into the import panel. Click import. If you have a lot of tabs, it can take hours. It may even choke if you have 1,000+ tabs. This worked for me with 1,025 tabs moving from Firefox to Edge browsers on the same Windows machine. You can also save the exported urls as a txt file and move it to a different machine, or even a different OS.
I was using the excellent Tree Style Tabs in Firefox to manage tabs, but discovered Edge has great support for tab groups and lets you put the tabs on the left side of the browser (like Tree Style Tabs) only with collapsible tab groups to keep things organized.
Longer term, I highly recommend Raindrop.io to manage the hundreds of tabs we all keep. Paid version adds nested tab groups ... awesome ... and they share easily across multiple devices/browsers. Organized, easy to get to from anywhere, and you don’t use half the RAM on your machine keeping all those tabs active. Very cool. No, I don’t work for Raindrop ... just a fan.