[scholia]

> No matter how many tabs I have open they remain usable size

They were! I think they've shrunk, though that might be an optical illusion... And I can't see a simple way to make them bigger (simple as in: not editing the css file).

[mythmon_]

There is a pref that controls the minimum width now (browser.tabs.tabMinWidth). The default changed from 100px to 76px in Firefox 57. You should be able to tweak this to change the minimum width.

[scholia]

Fantastic. Many many thanks.