1. Firefox 58 has considerable speed improvements
2. Firefox has much better support for tab customization like tree style tabs (not yet supported in 58, I think), multiple tabs, where you can close, move, reload multiple tabs together, copy url of selected tabs in custom format etc.
3. Reliable session recovery. With chrome , if you have more than one window each with multiple tabs, recovery of all windows is not guaranteed. Firefox on the other hand has a versatile session restore process. I sometimes have 6 or more nested session restores. Only thing affected is your sanity, when going through all the tabs. Also, in firefox, when recovering, the pages are not loaded unless the user purposefully navigates to the page, saving memory.
Firefox also supports hundreds of tabs easily. It is THE browser for tab hoarders.
4. Chrome on android does not allow extensions. So no ublock origin on Chrome mobile. That leaves a bad taste in the mouth. For that and other reasons cited by other answers here, I do not trust Chrome on desktop either.
5. Certain features on Web developer tools are better in firefox. I use both firefox and chrome for this interchangeably.
6. I like that typing in address bar checks only in history and bookmarks and the search bar is separate. In chrome, I often notice that search is given more priority over history. What is one hop in firefox becomes two in chrome: first to the search page, then the actual website.