diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 7ebb3dba8..53526098b 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -72,6 +72,12 @@ module ApplicationHelper
     text
   end
 
+  # A 1x1 transparent GIF, standing in for a real avatar when
+  # config.x.blank_avatars is set, which browser specs do: otherwise they fetch
+  # every avatar from gravatar.com for real, and one arriving mid-test moves
+  # whatever sits under it, so clicks land on the wrong thing.
+  BLANK_AVATAR = 'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7'
+
   #
   # Returns an image uri for a given member.
   #
@@ -79,6 +85,7 @@ module ApplicationHelper
   #
   def avatar_uri(member, size = 150)
     return unless member
+    return BLANK_AVATAR if Rails.configuration.x.blank_avatars
 
     if member.preferred_avatar_uri.present?
       # Some avatars support different sizes
diff --git a/app/views/members/_avatar.html.haml b/app/views/members/_avatar.html.haml
index b4ea132a9..a5e4ed80c 100644
--- a/app/views/members/_avatar.html.haml
+++ b/app/views/members/_avatar.html.haml
@@ -1 +1 @@
-= link_to image_tag(avatar_uri(member, 150), alt: "Avatar of #{member}", class: 'avatar img img-fluid'), member_path(member)
+= link_to image_tag(avatar_uri(member, 150), alt: "Avatar of #{member}", class: 'avatar img img-fluid', width: 150, height: 150), member_path(member)
diff --git a/app/views/members/_thumbnail.html.haml b/app/views/members/_thumbnail.html.haml
index dc9d7b9ca..e82cf5454 100644
--- a/app/views/members/_thumbnail.html.haml
+++ b/app/views/members/_thumbnail.html.haml
@@ -5,7 +5,7 @@
     / Avatar
     .avatar.mx-auto.white
       = link_to member do
-        = image_tag(avatar_uri(member, 150), class: 'rounded-circle img-fluid', alt: member)
+        = image_tag(avatar_uri(member, 150), class: 'rounded-circle img-fluid', alt: member, width: 150, height: 150)
     .card-body
       / Name
       %h4.card-title
diff --git a/spec/rails_helper.rb b/spec/rails_helper.rb
index bd64cd333..f20057711 100644
--- a/spec/rails_helper.rb
+++ b/spec/rails_helper.rb
@@ -117,20 +117,22 @@ RSpec.configure do |config|
   # Allow just create(:factory) instead of needing to specify FactoryBot.create(:factory)
   config.include FactoryBot::Syntax::Methods
 
-  # Prevent Poltergeist from fetching external URLs during feature tests
+  config.after(:each, :js) do
+    Rails.configuration.x.blank_avatars = false
+  end
+
   config.before(:each, :js) do
     # TODO: Why are we setting this page size then straight afterwards, maximising?
     width = 1920
     height = 1080
     Capybara.current_session.driver.browser.manage.window.resize_to(width, height)
 
-    if page.driver.browser.respond_to?(:url_blacklist)
-      page.driver.browser.url_blacklist = [
-        'gravatar.com',
-        'okfn.org',
-        'googlecode.com'
-      ]
-    end
+    # This used to block gravatar.com and friends through Poltergeist's
+    # url_blacklist. Poltergeist is long gone and Selenium's browser has no
+    # such method, so the guard was always false and the block never ran —
+    # every browser spec has been fetching avatars from gravatar.com for real.
+    # Stand them down instead, so nothing loads late and shifts the page.
+    Rails.configuration.x.blank_avatars = true
 
     # Historically, we wanted to .maximize; but this actually undoes the resize_to step above
     # with chrome headless