Doing some more digging, apparently AdGuard just created a URL tracking filter a couple of weeks ago that we should be able to enable in either the AdGuard or Ublock Origin (or perhaps other ad-blocking) Firefox mobile addons eventually: https://adguard.com/en/blog/adguard-url-tracking-filter.html

Or you can manually add the filter now. After installing the Ublock Origin addon in firefox mobile, I clicked on the 3 dots -> Addons -> Ublock Origin -> Open the dashboard -> Filter lists -> Import... and pasted this URL (from the top of the above link): https://raw.githubusercontent.com/AdguardTeam/FiltersRegistr...

I tested by sharing a URL with UTM and other parameters, and it did strip them.