In Thunderbird there's a horizontal scroll bar for the list of emails. It seems that this is related to the width of the lines: date, from, to subject, size, etc. In passing I note that some subject lines are huge; a subject line should be concise. There's an add-on to remove scroll bars hide_horizontal_scrollbar-0.2-tb,xpi This was downloaded into my data drive, and I copied it to my c:\thunderbird add-ons folder. I then used the method for installing XPI files, which I did fairly easily for the very nifty add-on that allows a user to edit the order of accounts and folders. The hide scrollbar XPI file did not come up when I searched. The XPI file manually_sort_folders-1.1.1-tb.xpi did not come up either.

Can someone please advise me how to install the hide scrollbar XPI? Thank you.