First of all, thanks for your work, I've been using Firefox for years, and I'm very happy. Unfortunately, after using Firefox 57 for a while and despite finding it very good, I have decided to revert to 56. I use an extension called Tile Tabs which allows me to display several tabs in a split window, even in full screen mode. That is very handy for me as I am a sports timer and often need to display several results lists on one screen in my browser based software. Since version 57, Tile Tabs is not supported anymore, I need to use Tile Tabs WE, which just creates separate windows for each tab. It would be great if you could release a new version of Web Extensions which could enable the Tile Tab developpers to add the same functionality to Tile Tabs WE, so I can use the latest version of my favorite browser, with my favorite extension. Until then, I'll stick with 56. Thanks for your attention. Cheers, Ugo https://addons.mozilla.org/en-US/firefox/addon/tile-tabs/