I have not yet encountered a browser that has this feature, but I'm often annoyed to leave my keyboard and to grab my mouse, just to reorder my tab bar.
It would be really nice to have a keyboard shortcut for that.
My proposal for the key combination to move a tab to the right or left would be:
- Command + Option + Shift + Left or Right
- and Command + Option + Shift + [ or ]
My favorite would be the first, because I already use Command + Option + Left or Right to switch tabs.
The second would also be fitting, because you can already change tabs by pressing Command + Shift + [ or ]