No vignettes found by browseVignettes where they actually are there

From Writing R Extensions, section 1.4.2, your vignettes need to have a line

%\VignetteEngine{knitr::knitr}

in them; a common paradigm is to add the following to the yaml at the top of the vignette

vignette: >
  %\VignetteIndexEntry{Integrating TCGA Data}
  %\VignetteEngine{knitr::rmarkdown}

VignetteIndexEntry provides a convenient title for R's help system. Remember the BiocStyle package for creating vignettes with a consistent look.