Hi,
As I feel I didn't gathered enough information to create a phabricator ticket, I send that here in order to obtain some guidance about what would be interesting to provide and how to get it. I can say that most of the time, I'm currently under Fedora 26 with Firefox 56, but that's probably not much relevant information.
So the problem is: when I edit a module, sometimes, but not systemically, the window at some point become sloooow. Like, there are large latency between typing and displaying of the resulting action. And indeed, for some reason, one processor core is around 100% due to a firefox thread.
As a side note, I would be interested with any advice to ease my module edit process, as the direct in-wiki edition and test become quickly frustrating. When I edit a basic wiki text, I often use "it's all text" which enable to edit in my usual text editor. But even this option won't work with the widget of code edition (the same problem occurs with "syntax highlight" extension).
Cheers