My last OPERA experience was v10.63.....I decided to switch to FireFox because I didn't like using menus...I wanted to use buttons...Custom Buttons is a breeze with FireFox (for what I want anyway), & I found customization much more user friendly in FireFox. Extensions were a dime a dozen,,,,Greasemonkey for userscripts gave me even more flexibility, & between the two I was able to find just about everything I could possibly ever want.
Opera then became one of my #1 goto browsers for specific sites, & saving websites easier.
I use FireFox Portable ESR v17.0.9 at present....but because it's portable, I don't have to search folders for anything....all my needs & files can be located independently in one folder.
Backups are as simple as copying a folder & it's contents.
Absolutely no Registry dependencies either.
If the browser should really get messed up, all I need to do is delete the folder, & copy the backup folder to replace it, or to wherever I want it located...I have over 7 versions of Firefox Portable from v3.6 all the way through v24.0 at my immediate disposal, & I can switch through all versions using any saved profile I wish.
I have basically one up to date profile that I can use with at least 15 different browsers simply by using a copy & paste, & they're always hot to go.
Then again, not often, but every once in a while I fall back on my OPERA browser due to a difficult rendering website.
I also have 3 versions of OPERA Portable available in a split second with just a simple toolbar custom button press.

Unless OPERA makes some monumental changes & u-turns, I doubt if I will ever go back to using it as my go to browser.
FireFox is getting a tad bit fussy with some of my must have custom buttons, but the Custom Button programmers are usually quick to the fix! Never had a button that couldn't be fixed or replaced with a better one.