Opera bug reports can be put
here, check the changelog for known bugs first though!
Glad your happy with the Dev i know theres a big community behind it i just don't do any Dev stuff so wouldn't really know, i only comment on what i actually know forwell!
You say this, but i don't understand, the installer is about the same size as firefox, it uses up same amount if not less memory than firefox with lots of tabs open, and it gives more features for that, how is that a bad thing? To get firefox to remember previous tabs you need to install 3rd party potentially dodgy code, to get it just to add x's to the tabs same again, for mouse gestures again same problem. The list goes on i agree its very easy to customise, but the amount of 3rd party extensions you need to get half the usability of opera inherrantly trips firefox up. As much as i like firefox opera is a more well rounded out of the box beast, but still customisable. For instance a lot of greasemonkey scripts still work with opera UserJS (it is more complicated i agree i think thyre sorting this too with a GUI). Content Block is a superb alternative to Adblocker another 3rd party! (again almost hidden more for legal reasons i assume).
Thats just my 2p though really what i've gathered over the years really...