In Firefox version 78, the Tab context menu was changed to add a new submenu. Inside of this submenu, options to and were added. Later on, a option was also added. This context menu can be viewed by right-clickinga secondary/two-finger click or holding down the control key while you click on a Firefox tab.
We made this change because the proximity of the menu items for closing tabs to the right and closing other tabs was causing some to accidentally close the wrong set of tabs, which resulted in a sub-par user experience. While there is anmenu item, some data may have been lost as well as potential increased network usage if the closed tabs were no longer in the Firefox cache.
The close tabs to the right feature was a first step towards providing more nuanced ways of managing tabs. In order to solve the problem of accidental tab closures and in the spirit of advancing functionality, theoption was moved into a submenu. The menu item provided an area to add functionality that people have asked for, such as close tabs to the left.
These context menus provide accessibility benefits for features that do not exist as keyboard shortcuts. That is why we took great care in introducing and removing them.
Alternatively, you can use an add-on to bring back the old menu, by searching for "Close other tabs" or similar terms at addons.mozilla.org. Two add-ons you can try are Close Tabs to the Right and Close Other Tabs.