Hi!
After Firefox and Chromium, there's a bunch of open source web browsers listed on [2], but a brief spot check showed many as being Linux only (or outdated Mac builds). One that looked promising was Brave[3], though it's a relatively new browser and I would need to do more research regarding #3.
I've been using Brave for a couple of months occasionally, and it seems to work pretty well. It has (some) adblocking in default config, and some other privacy-enhancing settings, which are probably not very important for Wikimedia sites but may either break some other sites or make them bearable :) It's pretty young, so I don't think we can say much about security record yet - IIRC it's based on Chromium, and it's updated pretty frequently, and it's easy to use (though the UI might be a bit more spartan then others for now, and not many extensions available - but for ex-IE users it may not be an issue).