I want to use a double-click (or a specific mouse button for double-click) to act like the Enter key in both the Linux terminal (e.g., KDE Terminal) and browser URL bars (Firefox/Chrome) or anywhere else.
3 Answers
That's not something that exists, I'm afraid: The input system can't know what you're double-clicking on (input fields are not "standardized" components, but the GUI library for every application implements that like it sees fit); so every program needs to be programmed how it should react to a double click individually.
I'm not aware for any browsers or extensions, or terminal emulators, where this would be implemented.
So I'm afraid and this can't be done (without rewriting a laaaarge amount of software).
Suggestion: See if bringing up a GUI keyboard app and clicking the Enter key on that app will do what you want. It's not a double-click in a URL entry field or a terminal window, but perhaps it could be a functional workaround for you.
As Marcus M said in a previous answer, there's no universal Linux setting for the double-click feature you're asking for. It would have to be a custom configuration setting in the GUI web browser and the GUI terminal emulator that you're using. There might possibly be browsers and terminal emulators with this kind of feature, but it's a very unusual feature and it's likely very few (if any) apps would have it.
If you are comfortable with programming, you may be able to write code in Autokey and Python.
The code would detect the double-click and replace it by a return
key press. There is an answer here that should get you started.