[mbudde]

A new version (0.15.20150902901) of TreeStyleTabs has been released that works with Firefox 42, but it will not automatically update so you need to install it from [1]. See also [2].

[1] https://addons.mozilla.org/en-US/firefox/addon/tree-style-ta...

[2] https://github.com/piroor/treestyletab/issues/973