Initial Opera 37 developer release is here for Windows, Mac and Linux, and is available to download. Opera says on its blog they’re readying two unknown surprises with this release, if they manage to fix everything on time. You can’t find these surprises either in the changelog or in the flags.
Opera 37 developer
Apart from unrevealed things, no-theme-overlay flag in this one lets you remove the overlay. Opera 36 is the last Chromium-based version that is going to run on Windows XP and Vista, Opera 37 won’t run on these older Windows OS. The Opera desktop team advises users on these older Windows to upgrade to more recent OS.