Mark unvisited tabs

[Skripa]

When opening multiple tabs, make a mark on the tabs that have not yet been visited

[Jon]

Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.

[Agentvirtuel]

Hello

https://connect.mozilla.org/t5/ideas/make-tabs-visually-distinguishable-from-another/idi-p/7295

Of course, it's not the answer expected, nevertheless.
If you wish to study Tab Mix Plus https://github.com/onemen/TabMixPlus

https://onemen.github.io/tabmixplus-docs/help/display-tab

Use the sidebar to access tools and vertical tabs
https://support.mozilla.org/en-US/kb/use-sidebar-access-tools-and-vertical-tabs

[igorlogius]

https://addons.mozilla.org/en-US/firefox/addon/unvisited-tabs-indicator/