stalebrim Do they really force Vivaldi, or does any Chrome-based browser work?
Don't know, but Brent's comment ("The wrinkle is this employer likes a 2FA for using (their/my zoom) that I have to type in at their website, on Vivaldi.") suggests that is the case.
But just in case the employer forces use of a Chrome-based browser rather than Vivaldi specifically, let me restate my comment:
The real problem is that this employer is forcing employees and contractors to use a Chrome-based browser in order to access 2FA on the employer's website. Would you even have Vivaldi on your computer if it weren't required for you to use a Chrome-based browser for this employer's 2FA?
I guess the question here is what browser Brent wants to use. If it is Vivaldi, then remove Firefox as the default browser or uninstall Firefox entirely. If it is Firefox, then removing Firefox or removing Firefox as his default browser will not work well for him.
In either case, the employer is not likely to change the requirement to access the employer's website via Vivaldi or a Chrome-based browser, as the case may be. So Brent is between a rock and a hard place if he prefers to use Firefox as his default browser. Changing the default browser is not a good solution in that case.