I prefer web interfaces rather than desktop clients when possible, i.e., when the web interface is at least almost as good as the desktop client, so I use the FastMail web app almost exclusively. For the most part, it's great. I would prefer not to be reprimanded for pinning ancient emails every time I look at my Archive, but whatever.
But let's talk about Compose.
Let's say I'm writing a rich text email, and I want to create a numbered list. I click the numbered list icon in the toolbar, and get a 1. I write something, newline, 2. Great. Write some more stuff. Now I want to start a sublist. Tab! Awesome. I add a few more sublist items. Now I want to dedent and add an item to the root list. Shift+tab! Wait, nope, that focuses the subject field. WTF? OK, scan the toolbar... nope, nothing there. Well, the ⏵¶ and ⏴¶ buttons look promising, but mouseover indicates they're for left-to-right / right-to-left text direction settings (how many people actually change text direction in an email?). Okay, hmm. Hack time! I go back to my root list and add a new item, and then copy & paste my sublist into the preceding root list item. Uggh, it's now all at the root list level. Let's try and indent them. Set the cursor to the beginning of the line... tab... nothing. Hmm. Create another pseudo-element, empty, above. Tab to indent, (fn+)delete to pull next root list item into sublist. Yay! It's a terrible, overwrought hack, but it works!
Mad props for not being the infuriating cesspit of UX that gmail has become, yet I can't help but think there might be a better way?
P.S.: Command + right bracket = quote. WTF#2? What text editor do your devs use that that seemed like a reasonable idiom?
P.P.S.: Chrome 46.0.2490.80, Mac OS X El Capitan
P.P.P.S.: Sorry to complain so much, but really, FastMail is great. I just wish it were better.