Concept works well.
Unfortunately, it's borderline unplayable in Firefox because Ctrl+W is a hard-coded keyboard shortcut that closes the current tab, immediately killing your run. With Ctrl being the dodge roll key and W is "move north," this will happen very frequently during a run. The Ctrl+W shortcut can't be disabled or worked around, unless you recompile Firefox.
I know Shift can also be used, but the keys are adjacent, so I still occasionally hit Ctrl+W by accident. Of course, I could alternatively use the arrow keys to move, but the right Shift / right Ctrl keys don't work as dodge roll buttons. My hand isn't big enough to use both arrow keys and left Shift / Ctrl at the same time, so in order to dodge while using the arrow keys, I either have to stop moving or stop shooting.
Easy to fix, though, just allow right Shift / Ctrl as dodge keys. That will allow actually using the arrow keys and fix the problem with accidentally closing the tab mid-run. Alternatively, you could add controller support.