Opera is a good browser, but to address your issue with RAM consumption I find that especially in Facebook your RAM won’t be released over time, if you keep a site like Yahoo, or anything for that matter set up as Homepage, and when your RAM usage climbs too high click “Home” and then “Back” after it loads, your RAM will be released.
I have Opera, Chromium, and Firefox, in addition to Chrome. I’ll use one of the others for another FB account I might be running simultaneously but I us Chrome and Chromium the most because they have the best Bookmarking setup of all the browsers…
If RAM isn’t an issue using the technique I mentioned then you have no real need to use a lighter browser
I hope this helps with your core issue