I am experiencing an issue with vertical tabs that appears once more than 3 tabs are open. This is happening on the ''.deb'' installation of ''Firefox'' (version 136.0) across 3 different devices, with different profiles, also when all extensions are disabled. The issue seems to be specific with vertical tabs, as it does not happen with the classical horizontal ones. The issue: In the vertical tabs sidebar I can move any tab up to any desired position. However, '''when moving a tab down, the next 2 positions are inaccessible''' (unless the lowest position in the sidebar is reached in less than 3 steps), it can only be moved to any position lower than that. Illustration: Assume you had 5 tabs open, named A, '''B''', C, D, and E. And let's assume you wanted to move tab B one position down to be situated between C and D. What I currently have to do to achieve that, is to move B below E (3 positions down: A, C, D, E, '''B'''), before I can move back up above D (2 positions up: A, C, '''B''', D, E). Seeing how tedious that is, I can only assume that it is unintended behavior caused either by a bug, or a setting (if so, which parameter in about:config should I look for?). Any suggestions to resolve this are appreciated.