I notice that this problem was reported way back in 2021, but rather than being resolved it was archived ! Well I suppose that's one way of whittling down problems logged on your stack of problems. I am using 103.0.1 on a Mac Mini running macOS Mojave. Like you, I'm being lazy and rather than typing a complete explanation of my own, I've simple cut and pasted the description from your previous complainant. This action is prevalent when I close the right-most tab and whammo, full screen which then causes me to have to mess around to get the window back to the size I WANT IT, and not full screen as your software would seem to want it ! **** Previous complaint **** Using latest version of Firefox for Mac (although this problem happened with some previous versions as well). When I have more than one tab open, and I click the X at the corner of a tab to close it, my Firefox window suddenly jumps to full screen. I have to drag the browser window from the edge to get it back to my original size. This behavior happens at other odd times as well, and the suddenly jumping to full screen gets really annoying. Any suggestions as to how I can fix this problem? **** End of previous complaint **** I suppose that one potential fix would be to ditch Firefox and revert to Safari, what do you reckon ? I wonder if Safari exhibits this extremely PERVERSE way of working ? Best regards Pete Findlow