I see this take a lot, usually revolving around "doing your part" to keep that tiny sliver of Firefox usage up in siteside metrics. Decide what's right for your case, but know that Waterfox and Firefox broadcast the same browser user agent so using WF doesn't take away "market share" from FF. The only thing using FF instead of WF does to "support firefox" is giving Mozilla Corp your data to "not sell, california just calls it selling" and your clicks on its built-in ads - if you're turning all that stuff off by hand it's the same as running WF.