Suddenly, beginning about three days ago, selecting a tab doesn't always then display that tab but instead the tab is selected in "multiple tab selection" mode WITHOUT pressing the CTRL key. Clicking on a tab highlights the tab instead of displaying the tab. Another click on the tab deselects the tab. Clicking on other tabs, selects rather than displaying them. Believe me, I understand what multiple tab selection is, how it works and how to correctly use it. This is not the case. I use tabs all day, every day and suddenly Firefox behaves erratically and randomly by selecting the tab and multiple tabs rather than displaying the tab selected. The workaround is to then select other tabs, deselect all tabs and then select the originally desired tab whereby the tab is displayed. If this is anomaly is unique me and only me, I will take my search to the Linux Cinnamon forums.