I uploaded the problematic Win7 profile at https://perfht.ml/2FjlFOy
So I see 96% of of the samples being spent in
mozilla::PresShell::Paint(nsView *,nsRegion const &,unsigned int)
void nsRefreshDriver::Tick(struct mozilla::layers::BaseTransactionId<mozilla::VsyncIdType>, class mozilla::TimeStamp)
and I don't see passwordManager.js at all which aligns with comment 8's suggestion that this isn't related to bug 1429560.
Just to double-check you don't have some unusual persisted <tree> value causing some inefficiency, can you rename xulstore.json to xulstore.json.bak in your profile folder while Firefox isn't running? Then see if the problem still happens. (You can put the file back afterwards as it keep tracks of positions and sizes of UI). You can access the profile folder from the about:support URL.
Thanks for providing the information :)