It is common for most people to have number of tabs open at the same time while browsing. However, Firefox only displays 10 tabs on the tabs bar. The other tabs are hidden and has to be scrolled by clicking on the small arrow on the right of the tabs bar. The idea is that if too many tabs are displayed, the tabs will shrink so much that it would be difficult to identify the tabs. However, it is not very convenient to keep scrolling for the hidden tabs.
Now, a new extension for Firefox is taking shape which will make things pretty easy to work with lot of tabs.
Enter Tab Groups. It is presently in the pre-Alpha stage at version 0.02. I installed and tried it and it seems to work without any problems.
As the name implies, Tab Groups actually helps you organize your tabs into groups. So you can conveniently group your tabs according to their subject or any other factor you find fit and see only the tabs of one group at a time. This greatly reduces the clutter and I find it to be immensely useful. You can even rename the group tabs and also drag tabs from one group to another. New tabs are opened in the current group.
Tab Group supports Session store. So if Firefox crashes, the next time you open Firefox, all your Group Tabs with their Page Tabs are intact.
Presently, Tab Groups has only basic functionality but a lot of features are slated to be added in the future.