This morning I opened Firefox only to find that the GUI had changed completely. I have managed to enable the theme and have customised the toolbar, but my extensions are no longer visibile to the right of the search box, and my dictionaries and language packs are disabled without (so it seems) the possibility of enabling them. My bookmarks seem to be intact, but Firefox is now extremely slow (I've been waiting ages for a new tab to open). What is going on, and how can I restore my extensions (including password manager) and language tools?