Loved Opera back in the day. It had "page specific settings" that would let me allow to set HTTP/Socks5 proxies on a per-page setting - today you cannot even set a proxy anymore without changing your system settings (not browser settings).
If anyone asks, I used this heavily to bypass country blocks/redirects on a per-page level and also with privoxy on some privacy invading sites.
And don't forget the ability to run a web server from within the browser. Opera was sometimes buggy, but it was really the first "browser as an operating system".
foxyproxy does this. i set up a ssh passthrough and routed foxyproxy with only specifed pages to use local proxy which meant they would be routed through the ssh. it worked for what i wanted
If anyone asks, I used this heavily to bypass country blocks/redirects on a per-page level and also with privoxy on some privacy invading sites.