I'm on TB 60 on Win10x64Pro Originally I was trying to install the theme-and-font-size-changer-for-tb, but installing it via the add-ons tab results in there being no font size options on the add-on's option menu. So I decided to download the add-on and install from disk to see if that would work. I was unable to find any method of doing that in the add-ons tab, so I searched the support forums and came up with this forum message https://support.mozilla.org/en-US/kb/installing-addon-thunderbird However, my add-ons tab does not look like what that post says to expect. The attached image is what I see on the add-ons tab. The quoted post says to look for the gear (tools menu) but there is no such icon on my screen, and no option to "Install Add-on from File" on the standard Tools menu. Next I tried the shift-launch and "Reset Toolbars and Controls" but nothing changes. So then I tried starting in "Safe Mode", but still the add-ons tab looks the same, with no way to install from a file. Is this an interaction between Win10 and TB 60? Should there be a tools menu on the add-ons tab? If not, how does one install an add-on from a downloaded file?