Mostly, the syntax highlighting mode is fine in a few or several (if not most) non-Microsoft browsers.
One issue with using the mode in Chrome and/or Opera is dragging and dropping a content while editing an article or a page. When I double-click on either one word, line, or paragraph, and I drag it to another place, the dragged text content is no longer highlighted. This means that I cannot continually drag and drop a content from one place to another. Therefore, I have to redo the dragging and dropping every time this happens repeatedly. It occurs at 2003, 2006, and 2010 WikiEditors while using the syntax highlighting mode.
On the contrary, 2017 WikiEditor has no issues with dragging and dropping while running the feature; the dragged content stays highlighted, so I can continue dragging a content. Furthermore, In Firefox, continuing the dragging-and-dropping action works all right in all WikiEditors.
Nonetheless, while in this mode in a non-Microsoft browser, an action cannot be undone because "Undo" either is not working or is unavailable while in this mode.