Closer to Geany or Sublime. I haven't used gedit before though. Kate has language server back end integration, add-on support, integrated terminal, and other features. Geany might be a good option, though I know nothing of its speed. Kate seemed fine but again no idea.
Firefox resistant fingerprinting does the first 2 things, the last one is mobile partial letterboxing. All are anti fingerprinting techniques, but i understand how they may be restrictive. Maybe just add dark reader to have dark mode forced on websites, which technically can be fingerprinted but has a large userbase so idk.
What about a chromebox flashed with some linux os? Nice and cheap mini x86 pc. Just picked one up for 35 bucks with an i7 6th gen, just hoping it uses sodimm and isnt integrated on the mobo.
Mull works the same as Fennec, except it is hardended with patches from Tor and Arkenfox user.js. No real reason IMO to use fennec over Mull, whose developers also contribute to Fennec. Ghostery also changes your fingerprint, acting as one more data point.
Mull has a whole bunch of configured flags to reduce fingerprinting, and many more to help with security (like disabling JIT).