Windows – Is it possible to run Chrome with and without web security at the same time

open -a "Google Chrome" --args --allow-file-access-from-files

I don't know how to adequately test the --allow-file-access-from-files switch, but it works for --incognito for me (same version and OS).

It appears as though Chrome does not like to be opened twice; when passing the -n switch to open (which is supposed to open a new instance), it immediately kills itself.

EDIT: 'allow-files-access-from-files' should be 'allow-file-access-from-files'

The --single-process option you've found is not officially supported, so it's not guaranteed to work, may still use more than a single process and may cause additional performance or stability issues.

There are a couple of other Chromium options you could use instead:

1. Since Chromium 67 you may want to disable Site Isolation using --disable-site-isolation-trials command line option or the following flag: chrome://flags/#site-isolation-trial-opt-out. This will force subframes to run in their pages' processes and allow you to use the next option;
2. You could explicitly limit the amount of renderer processes using --renderer-process-limit=2 command line option. It will force all the tabs and extensions to use a single process (per each type);
3. The --in-process-gpu option will run the GPU process as a thread in the main browser process. These processes consume most of the CPU time and the GPU driver crash will likely crash the whole browser, so you probably don't wanna use it.

Warning!
Most of these options will reduce the security of your browser! You use them at your own risk.

I was testing these options on Vivaldi 3.3 (Chrome 85) with 5 Super User tabs, 3 other tabs and 4 extensions. Here are the results I've got:

Default:                                    24 processes
Default - Site Isolation:                   19 processes
Default - Site Isolation + Renderer Limit:  10 processes