diff --git a/scss/global.scss b/scss/global.scss
index 5c1c8783..31879ff0 100644
--- a/scss/global.scss
+++ b/scss/global.scss
@@ -29,13 +29,24 @@ body {
   line-height: 1.4;
   color: var(--body-text-color);
   background: var(--body-bg);
-  -webkit-tap-highlight-color: transparent; /* fix for blue background on spoiler tap on Chrome for Android */
+  -webkit-tap-highlight-color: transparent; // fix for blue background on spoiler tap on Chrome for Android
+  @supports not (-webkit-overflow-scrolling: touch) {
+    // Prevent horizontal scrolling on mobile Firefox on small screens. See below for why we're
+    // using a @supports here to target non-iOS browsers.
+    overflow-x: hidden;
+  }
 }
 
 .main-content {
-  // these margins should be kept in sync with getMainTopMargin.js
+  @supports (-webkit-overflow-scrolling: touch) {
+    // iOS Safari ignores overflow-x:hidden on body, so we add it again here. Unfortunately, this breaks the display
+    // of the position:sticky button in Chrome, so we wrap it in a @supports query that only targets iOS
+    // See https://stackoverflow.com/a/14271049
+    overflow-x: hidden;
+  }
+  contain: content; // see https://www.w3.org/TR/2018/CR-css-contain-1-20181108/#valdef-contain-content
+  // these paddings should be kept in sync with getMainTopMargin.js
   padding-top: 42px;
-  contain: content; /* see https://www.w3.org/TR/2018/CR-css-contain-1-20181108/#valdef-contain-content */
   @media (max-width: 991px) {
     padding-top: 52px;
   }
diff --git a/templates/2xx.html b/templates/2xx.html
index 9e63b660..1ff0d740 100644
--- a/templates/2xx.html
+++ b/templates/2xx.html
@@ -17,7 +17,7 @@
   <style>
 /* auto-generated w/ build-sass.js */
 body{--button-primary-bg: #6081e6;--button-primary-text: #fff;--button-primary-border: #132c76;--button-primary-bg-active: #456ce2;--button-primary-bg-hover: #6988e7;--button-bg: #e6e6e6;--button-text: #333;--button-border: #a7a7a7;--button-bg-active: #bfbfbf;--button-bg-hover: #f2f2f2;--input-border: #dadada;--anchor-text: #4169e1;--main-bg: #fff;--body-bg: #e8edfb;--body-text-color: #333;--main-border: #dadada;--svg-fill: #4169e1;--form-bg: #f7f7f7;--form-border: #c1c1c1;--nav-bg: #4169e1;--nav-border: #214cce;--nav-a-border: #4169e1;--nav-a-selected-border: #fff;--nav-a-selected-bg: #6d8ce8;--nav-svg-fill: #fff;--nav-text-color: #fff;--nav-a-selected-border-hover: #fff;--nav-a-selected-bg-hover: #839deb;--nav-a-bg-hover: #577ae4;--nav-a-border-hover: #4169e1;--nav-svg-fill-hover: #fff;--nav-text-color-hover: #fff;--action-button-fill-color: #90a8ee;--action-button-fill-color-hover: #a2b6f0;--action-button-fill-color-active: #577ae4;--action-button-fill-color-pressed: #2351dc;--action-button-fill-color-pressed-hover: #3862e0;--action-button-fill-color-pressed-active: #1d44b8;--action-button-deemphasized-fill-color: #666;--action-button-deemphasized-fill-color-hover: #9e9e9e;--action-button-deemphasized-fill-color-active: #737373;--action-button-deemphasized-fill-color-pressed: #545454;--action-button-deemphasized-fill-color-pressed-hover: #616161;--action-button-deemphasized-fill-color-pressed-active: #404040;--settings-list-item-bg: #fff;--settings-list-item-text: #4169e1;--settings-list-item-text-hover: #4169e1;--settings-list-item-border: #dadada;--settings-list-item-bg-active: #e6e6e6;--settings-list-item-bg-hover: #fafafa;--toast-bg: #333;--toast-border: #fafafa;--toast-text: #fff;--mask-bg: #333;--mask-svg-fill: #fff;--mask-opaque-bg: rgba(51,51,51,0.8);--loading-bg: #ededed;--account-profile-bg-backdrop-filter: rgba(255,255,255,0.7);--account-profile-bg: rgba(255,255,255,0.9);--deemphasized-text-color: #666;--focus-outline: #c5d1f6;--very-deemphasized-link-color: rgba(65,105,225,0.6);--very-deemphasized-text-color: rgba(102,102,102,0.6);--status-direct-background: #d2dcf8;--main-theme-color: #4169e1;--warning-color: #e01f19;--alt-input-bg: rgba(255,255,255,0.7);--muted-modal-bg: transparent;--muted-modal-focus: #999;--muted-modal-hover: rgba(255,255,255,0.2);--compose-autosuggest-item-hover: #ced8f7;--compose-autosuggest-item-active: #b8c7f4;--compose-autosuggest-outline: #dbe3f9;--compose-button-halo: rgba(255,255,255,0.1)}
-@font-face{font-family:PinaforeRegular;src:local("BlinkMacSystemFont"),local("Segoe UI"),local("Roboto"),local("Oxygen-Sans"),local("Ubuntu"),local("Cantarell"),local("Fira Sans"),local("Droid Sans"),local("Helvetica Neue")}@font-face{font-family:PinaforeEmoji;src:local("Apple Color Emoji"),local("Segoe UI Emoji"),local("Segoe UI Symbol"),local("Twemoji Mozilla"),local("Noto Color Emoji"),local("EmojiOne Color"),local("Android Emoji")}body{margin:0;font-family:system-ui, -apple-system, PinaforeRegular, sans-serif;font-size:14px;line-height:1.4;color:var(--body-text-color);background:var(--body-bg);-webkit-tap-highlight-color:transparent}.main-content{padding-top:42px;contain:content}@media (max-width: 991px){.main-content{padding-top:52px}}@media (max-width: 767px){.main-content{padding-top:62px}}main{position:relative;width:602px;max-width:100vw;padding:0;box-sizing:border-box;margin:30px auto 15px;background:var(--main-bg);border:1px solid var(--main-border);border-radius:1px;min-height:70vh}@media (max-width: 767px){main{margin:5px auto 15px}}footer{width:602px;max-width:100vw;box-sizing:border-box;margin:15px auto;border-radius:1px;background:var(--main-bg);font-size:0.9em;padding:20px;border:1px solid var(--main-border)}h1,h2,h3,h4,h5,h6{margin:0 0 0.5em 0;font-weight:400;line-height:1.2}h1{font-size:2em}a{color:var(--anchor-text);text-decoration:none}a:visited{color:var(--anchor-text)}a:hover{text-decoration:underline}input{border:1px solid var(--input-border);padding:5px;box-sizing:border-box}input[type=search]{-webkit-appearance:none}input,textarea{background:inherit;color:inherit}textarea{font-family:system-ui, -apple-system, PinaforeRegular, sans-serif, PinaforeEmoji}button,.button{font-size:1.2em;background:var(--button-bg);border-radius:2px;padding:10px 15px;border:1px solid var(--button-border);cursor:pointer;color:var(--button-text)}button:hover,.button:hover{background:var(--button-bg-hover);text-decoration:none}button:active,.button:active{background:var(--button-bg-active)}button[disabled],.button[disabled]{opacity:0.35;pointer-events:none;cursor:not-allowed}button.primary,.button.primary{border:1px solid var(--button-primary-border);background:var(--button-primary-bg);color:var(--button-primary-text)}button.primary:hover,.button.primary:hover{background:var(--button-primary-bg-hover)}button.primary:active,.button.primary:active{background:var(--button-primary-bg-active)}p,label,input{font-size:1.3em}ul,li,p{padding:0;margin:0}.hidden{opacity:0}*:focus{outline:2px solid var(--focus-outline)}.container:focus{outline:none}button::-moz-focus-inner{border:0}input:required,input:invalid{box-shadow:none}textarea{font-family:inherit;font-size:inherit;box-sizing:border-box}@keyframes spin{0%{transform:rotate(0deg)}25%{transform:rotate(90deg)}50%{transform:rotate(180deg)}75%{transform:rotate(270deg)}100%{transform:rotate(360deg)}}.spin{animation:spin 1.5s infinite linear}.ellipsis::after{content:"\2026"}.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0, 0, 0, 0);border:0}.inline-custom-emoji{width:1.4em;height:1.4em;margin:-0.1em 0;object-fit:contain;vertical-align:middle}.inline-emoji{font-family:PinaforeEmoji, sans-serif}
+@font-face{font-family:PinaforeRegular;src:local("BlinkMacSystemFont"),local("Segoe UI"),local("Roboto"),local("Oxygen-Sans"),local("Ubuntu"),local("Cantarell"),local("Fira Sans"),local("Droid Sans"),local("Helvetica Neue")}@font-face{font-family:PinaforeEmoji;src:local("Apple Color Emoji"),local("Segoe UI Emoji"),local("Segoe UI Symbol"),local("Twemoji Mozilla"),local("Noto Color Emoji"),local("EmojiOne Color"),local("Android Emoji")}body{margin:0;font-family:system-ui, -apple-system, PinaforeRegular, sans-serif;font-size:14px;line-height:1.4;color:var(--body-text-color);background:var(--body-bg);-webkit-tap-highlight-color:transparent}@supports not (-webkit-overflow-scrolling: touch){body{overflow-x:hidden}}.main-content{contain:content;padding-top:42px}@supports (-webkit-overflow-scrolling: touch){.main-content{overflow-x:hidden}}@media (max-width: 991px){.main-content{padding-top:52px}}@media (max-width: 767px){.main-content{padding-top:62px}}main{position:relative;width:602px;max-width:100vw;padding:0;box-sizing:border-box;margin:30px auto 15px;background:var(--main-bg);border:1px solid var(--main-border);border-radius:1px;min-height:70vh}@media (max-width: 767px){main{margin:5px auto 15px}}footer{width:602px;max-width:100vw;box-sizing:border-box;margin:15px auto;border-radius:1px;background:var(--main-bg);font-size:0.9em;padding:20px;border:1px solid var(--main-border)}h1,h2,h3,h4,h5,h6{margin:0 0 0.5em 0;font-weight:400;line-height:1.2}h1{font-size:2em}a{color:var(--anchor-text);text-decoration:none}a:visited{color:var(--anchor-text)}a:hover{text-decoration:underline}input{border:1px solid var(--input-border);padding:5px;box-sizing:border-box}input[type=search]{-webkit-appearance:none}input,textarea{background:inherit;color:inherit}textarea{font-family:system-ui, -apple-system, PinaforeRegular, sans-serif, PinaforeEmoji}button,.button{font-size:1.2em;background:var(--button-bg);border-radius:2px;padding:10px 15px;border:1px solid var(--button-border);cursor:pointer;color:var(--button-text)}button:hover,.button:hover{background:var(--button-bg-hover);text-decoration:none}button:active,.button:active{background:var(--button-bg-active)}button[disabled],.button[disabled]{opacity:0.35;pointer-events:none;cursor:not-allowed}button.primary,.button.primary{border:1px solid var(--button-primary-border);background:var(--button-primary-bg);color:var(--button-primary-text)}button.primary:hover,.button.primary:hover{background:var(--button-primary-bg-hover)}button.primary:active,.button.primary:active{background:var(--button-primary-bg-active)}p,label,input{font-size:1.3em}ul,li,p{padding:0;margin:0}.hidden{opacity:0}*:focus{outline:2px solid var(--focus-outline)}.container:focus{outline:none}button::-moz-focus-inner{border:0}input:required,input:invalid{box-shadow:none}textarea{font-family:inherit;font-size:inherit;box-sizing:border-box}@keyframes spin{0%{transform:rotate(0deg)}25%{transform:rotate(90deg)}50%{transform:rotate(180deg)}75%{transform:rotate(270deg)}100%{transform:rotate(360deg)}}.spin{animation:spin 1.5s infinite linear}.ellipsis::after{content:"\2026"}.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0, 0, 0, 0);border:0}.inline-custom-emoji{width:1.4em;height:1.4em;margin:-0.1em 0;object-fit:contain;vertical-align:middle}.inline-emoji{font-family:PinaforeEmoji, sans-serif}
 body.the-body.offline{--button-primary-bg: #ababab;--button-primary-text: #fff;--button-primary-border: #4d4d4d;--button-primary-bg-active: #9c9c9c;--button-primary-bg-hover: #b0b0b0;--button-bg: #e6e6e6;--button-text: #333;--button-border: #a7a7a7;--button-bg-active: #bfbfbf;--button-bg-hover: #f2f2f2;--input-border: #dadada;--anchor-text: #999;--main-bg: #fff;--body-bg: #fafafa;--body-text-color: #333;--main-border: #dadada;--svg-fill: #999;--form-bg: #f7f7f7;--form-border: #c1c1c1;--nav-bg: #999;--nav-border: gray;--nav-a-border: #999;--nav-a-selected-border: #fff;--nav-a-selected-bg: #b3b3b3;--nav-svg-fill: #fff;--nav-text-color: #fff;--nav-a-selected-border-hover: #fff;--nav-a-selected-bg-hover: #bfbfbf;--nav-a-bg-hover: #a6a6a6;--nav-a-border-hover: #999;--nav-svg-fill-hover: #fff;--nav-text-color-hover: #fff;--action-button-fill-color: #c7c7c7;--action-button-fill-color-hover: #d1d1d1;--action-button-fill-color-active: #a6a6a6;--action-button-fill-color-pressed: #878787;--action-button-fill-color-pressed-hover: #949494;--action-button-fill-color-pressed-active: #737373;--action-button-deemphasized-fill-color: #666;--action-button-deemphasized-fill-color-hover: #9e9e9e;--action-button-deemphasized-fill-color-active: #737373;--action-button-deemphasized-fill-color-pressed: #545454;--action-button-deemphasized-fill-color-pressed-hover: #616161;--action-button-deemphasized-fill-color-pressed-active: #404040;--settings-list-item-bg: #fff;--settings-list-item-text: #999;--settings-list-item-text-hover: #999;--settings-list-item-border: #dadada;--settings-list-item-bg-active: #e6e6e6;--settings-list-item-bg-hover: #fafafa;--toast-bg: #333;--toast-border: #fafafa;--toast-text: #fff;--mask-bg: #333;--mask-svg-fill: #fff;--mask-opaque-bg: rgba(51,51,51,0.8);--loading-bg: #ededed;--account-profile-bg-backdrop-filter: rgba(255,255,255,0.7);--account-profile-bg: rgba(255,255,255,0.9);--deemphasized-text-color: #666;--focus-outline: #bfbfbf;--very-deemphasized-link-color: rgba(153,153,153,0.6);--very-deemphasized-text-color: rgba(102,102,102,0.6);--status-direct-background: #ededed;--main-theme-color: #999;--warning-color: #e01f19;--alt-input-bg: rgba(255,255,255,0.7);--muted-modal-bg: transparent;--muted-modal-focus: #999;--muted-modal-hover: rgba(255,255,255,0.2);--compose-autosuggest-item-hover: #c4c4c4;--compose-autosuggest-item-active: #b8b8b8;--compose-autosuggest-outline: #ccc;--compose-button-halo: rgba(255,255,255,0.1)}
 
 </style>