Android: Tabs merging

No, there's no tab grouping on Firefox for Android. I have not found an extension that works for mobile for that functionality either.

Firefox on mobile does have something called Collections. It's not a tab group, but like a group of bookmarks you can save.

I wish, one of the features I miss from Chrome.

Maybe Fennec (a Firefox fork that lets you install desktop add-ons) and this https://addons.mozilla.org/en-US/firefox/addon/simple-tab-groups/.