Could be caused by broken code in userChrome.css in case you use this file.

Are you using userChrome.css to modify the position of the Tab bar?

• https://www.userchrome.org/what-is-userchrome-css.html
• https://www.userchrome.org/how-create-userchrome-css.html

You will have to look for updated code that works with Firefox 68.

Can you post your current code ?

Hello, thank you for the reply. Below is my current userChrome.css code. I created this some years ago when FF started moving the various bars around. I also used to use TabMixPlus, but that is no longer compatible with FF. Any suggestions to 1) make FF usable and 2) give me the ideal state of file/location bar at the top, then bookmark bar, then tabs (multirow, uniform size if possible) would be greatly appreciated.

/* tabs on bottom */ #navigator-toolbox toolbar:not(#nav-bar):not(#toolbar-menubar) {-moz-box-ordinal-group:10} #TabsToolbar {-moz-box-ordinal-group:1000!important}
.tabbrowser-tab:not([pinned]) {min-width:35px;max-width:35px;}
.tabbrowser-tab,.tab-background {height:var(--tab-min-height);}
.tab-stack {width: 100%;}
#tabbrowser-tabs .scrollbox-innerbox {display: flex;flex-wrap: wrap;}
#tabbrowser-tabs .arrowscrollbox-scrollbox {overflow: visible;display: block;}
#titlebar,#titlebar-buttonbox{height:var(--tab-min-height) !important;}
#titlebar{margin-bottom:calc(var(--tab-min-height)*-1) !important;}
#main-window[sizemode="maximized"] #titlebar{margin-bottom:calc(6px + var(--tab-min-height)*-1) !important;}
#main-window[sizemode="maximized"] #TabsToolbar{margin-left:var(--tab-min-height);}
#titlebar:active{margin-bottom:0 !important;}
#titlebar:active #titlebar-content{margin-bottom:var(--tab-min-height) !important;}
#tabbrowser-tabs .scrollbutton-up,.tabbrowser-tabs .scrollbutton-down,#alltabs-button,.tabbrowser-tab:not([fadein]){display: none;}

Hi Not applicable, you could look at the rules from the author of Classic Theme Restorer. I made a couple extracts here for Windows:

• Firefox 70: https://www.userchrome.org/samples/userChrome-tabs_on_bottom_Fx70.css
• Firefox 65: https://www.userchrome.org/samples/userChrome-tabs_on_bottom_Fx65.css

See also this thread for updated userChrome.css code for Firefox 65+ to move the Tab bar to the bottom position.

• /questions/1248277#answer-1192325

Many thanks! Finally had a chance to implement the solution and it worked like a charm. Hooray!