There’s also the grand-unified browser, a combination of an Arkenfox-ed qube and split browser. ( How to have VM start on boot in the background? - General Discussion - Qubes OS Forum (qubes-os.org) )
If you want extensions pre-installed there will be some fingerprinting (because the mere fact that you have them installed is part of what sites see) but with some effort you can at least avoid having the same profile show up every time (which is unique to you once generated). You’ll look like you could be anyone with the same taste in extensions.
One thing you can do, if there is some extension you like but don’t use very often, is to create one VM where it is installed, and another one just like it except that it is NOT installed. Then run that latter one except when you need the extension in question. That reduces your uniqueness online except for when you need that extension.