Currently, .ft files don’t open in Quicklook. It would really help me out if they did. Thanks!
Chris
I have it on my system working fine, but I have many quick look filters installed. If you use HomeBrew with Casks, you can install them. Get the full list using brew cask search ql. The qlmarkdown allows viewing of all markdown files.
FoldingText doesn’t have any built in specialized quick look support… but it does declare FoldingText files as plaintext, so minimally you should be able to quick look preview them and see the plain text content. (As mentioned above you can also get other Markdown quick look plugins to display formatted versions of that text with some configuration).
If you are seeing no quick look preview at all… I think there was an issue where if you had the TextMate beta installed it would break quick look support for FoldingText files. So if that’s the problem you are seeing maybe try to delete TextMate?
No luck with QLMarkdown—QuickLook still shows only an icon. And while I do like FoldingText, I don’t like it enough to delete TextMate. 
Any suggestions for how to make the two get along?
If I remember correctly the issue is that TextMate is trying to generate a QuickLook view for .ft files, but it crashes in the process, and so you don’t see anything. Try saving your FoldingText document with a different file extension, I think that might avoid the issue.
I think, perhaps you should contact TextMate and let them know about the bug with QuickLook support.
I can confirm that I did have this same issue, and removing TextMate beta fixed the problem for me. Since you say you can’t do that, perhaps there is a way to find the TextMate QL generator and delete it. But really, you should file a bug with Allan on this.
Found the TextMateQL.qlgenerator and made it unrecognizable to the system. QuickLook is now displaying .ft files. Yay! I’ll file a bug report with TextMate.
Thanks!