Rated 1 out of 5 stars

in FF
disconnect from sync service
unactivate kwallet plugin
restart FF

check that kwallet plugin is well unactivated

connect to sync service
go to FF password manager
copy somewhere the password of "Chrome://FirefoxAccounts (Firefox Accounts credentials)"
activate kwallet plugin

in kwallet manager replace the password of "Chrome://FirefoxAccounts" by the password you copied somewhere

restart FF

enjoy !

my explication : passwords(tokens) delivered with or without kwallet manager activated are different

with kwallet activated
{"version":1,"accountData":{"sessionTokenContext":"fx_desktop_v1","unwrapBKey":"d92...fe7","keyFetchToken":"6vg...3eb","customizeSync":false}}

with kwallet unactivated
{"version":1,"accountData":{"sessionTokenContext":"fx_desktop_v1","customizeSync":false,"kA":"65...09","kB":"01...46"}}

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