I've used Opera since the days you could open the binary in a hexeditor to disable the ad-support, from memory that was 1996 or so. I've been sore to see it become a chromium skin and am still hanging on to it out of a kind of inertia. The combination of Opera with my kid does nasty things with the memory though (he likes to open about 5 tabs with googlemaps and up to another 10 with youtube and umpty wiki's. With all mem&swap full, linux becomes unresponsive. It's a shame that this still happens in 2016, I say). Otherwise I use FF sometimes. I've tried more minimalistic browsers which has a certain appeal but I also want them to 'just work and display the page', so I've never actually made the switch.

Kirby: doesn't Debian supply security fixes? I thought the difficulty of backporting to really old versions was their reason for switching to the latest LTS version. But I've been gone from Debian for some time. Anyway, Iceweasel is rebranded Firefox so I'm not sure what you hope to achieve by such a switch.