I've been using SQL Developer for about a decade, and never felt compelled to post anything before this. Let me just say that the new "feature" is atrocious.
Here is just a small set of reasons why this functionality is less capable / more cumbersome / below industry standards in just about every imaginary way.
1. CTRL-F does not bring up the Search and Replace panel, only Search. It takes either mouse activity or several keystrokes to bring up Replace
2. You cannot effectively navigate through the new "tool" using just keystrokes
3. The search and replace text entry windows are tiny and not resizable
4. The search and replace tool is no longer in a floating window, so you can't put it on another monitor - you are forced to accept less visible editor space
5. Oftentimes when a searched-for string is in quotes in the body of the editor, Search will not find it no matter how hard you try - this is a severe bug
6. It is typical to work on roll out and rollback scripts simultaneously. In the past, if you had a change to make in both you would of course have to enter the Search/Replace phrases for the first window but it would remember them for the second so you could simply repeat the replace. Now every window has it's own "Search and Replace Instance," and each instance is equally stupid and annoying.
7. In previous versions if you double-clicked on a word or phrase, that word or phrase was then highlighted throughout the script. Over-writing one instance of that word or phrase left the remaining instances still highlighted, so you could selectively paste over those you were looking for. Now, you have to Search again to find each instance. This may not specifically be search and replace functionality, but is related
There are literally thousands of applications on the market with better search and replace functionality which Oracle might have drawn upon for inspiration - either to be more like market leaders or to use ones which were truly easier to use as well as more versatile. Instead they seem to have been determined to make SQL Developer as hard to use as possible.