refactor(nvim): set markdown browser to firefox

dots/.nvim-environments/primary/config/lua/plugins/plugins.lua

@@ -547,6 +547,7 @@ return packer.startup({
             run = "cd app && npm install",
             setup = function()
                 vim.g.mkdp_filetypes = { "markdown" }
+                vim.g.mkdp_browser = "firefox"
             end,
             ft = { "markdown" },
         })