diff --git a/src/utils/highlightMatching/domUtils.ts b/src/utils/highlightMatching/domUtils.ts
index 594bf9b1..c8c1fafb 100644
--- a/src/utils/highlightMatching/domUtils.ts
+++ b/src/utils/highlightMatching/domUtils.ts
@@ -64,10 +64,36 @@ export function tryMarkInTextNodes(
     let actualIndex = index
     if (useNormalized) {
       // Map normalized index back to original text
-      let normalizedIdx = 0
-      for (let i = 0; i < text.length && normalizedIdx < index; i++) {
-        if (!/\s/.test(text[i]) || (i > 0 && !/\s/.test(text[i-1]))) normalizedIdx++
-        actualIndex = i + 1
+      // Build normalized text while tracking original positions
+      let normalizedPos = 0
+      let prevWasWs = false
+      for (let i = 0; i < text.length; i++) {
+        const ch = text[i]
+        const isWs = /\s/.test(ch)
+        
+        if (isWs) {
+          // Whitespace: count only at start of whitespace sequence
+          if (!prevWasWs) {
+            if (normalizedPos === index) {
+              actualIndex = i
+              break
+            }
+            normalizedPos++
+          }
+          prevWasWs = true
+        } else {
+          // Non-whitespace: count each character
+          if (normalizedPos === index) {
+            actualIndex = i
+            break
+          }
+          normalizedPos++
+          prevWasWs = false
+        }
+      }
+      // If we didn't find exact match, use last position
+      if (normalizedPos < index) {
+        actualIndex = text.length
       }
     }
     
diff --git a/src/utils/highlightMatching/htmlMatching.ts b/src/utils/highlightMatching/htmlMatching.ts
index 05ec73f6..1c72eda2 100644
--- a/src/utils/highlightMatching/htmlMatching.ts
+++ b/src/utils/highlightMatching/htmlMatching.ts
@@ -1,6 +1,54 @@
 import { Highlight } from '../../types/highlights'
 import { tryMarkInTextNodes } from './domUtils'
 
+interface CacheEntry {
+  html: string
+  timestamp: number
+}
+
+// Simple in-memory cache for highlighted HTML results
+const highlightCache = new Map<string, CacheEntry>()
+const CACHE_TTL = 5 * 60 * 1000 // 5 minutes
+const MAX_CACHE_SIZE = 50 // FIFO eviction after this many entries
+
+/**
+ * Generate cache key from content and highlights
+ */
+function getCacheKey(html: string, highlights: Highlight[], highlightStyle: string): string {
+  // Create a stable key from content hash (first 200 chars) and highlight IDs
+  const contentHash = html.slice(0, 200).replace(/\s+/g, ' ').trim()
+  const highlightIds = highlights
+    .map(h => h.id)
+    .sort()
+    .join(',')
+  return `${contentHash.length}:${highlightIds}:${highlightStyle}`
+}
+
+/**
+ * Clean up old cache entries and enforce size limit
+ */
+function cleanupCache(): void {
+  const now = Date.now()
+  const entries = Array.from(highlightCache.entries())
+  
+  // Remove expired entries
+  for (const [key, entry] of entries) {
+    if (now - entry.timestamp > CACHE_TTL) {
+      highlightCache.delete(key)
+    }
+  }
+  
+  // Enforce size limit with FIFO eviction (oldest first)
+  if (highlightCache.size > MAX_CACHE_SIZE) {
+    const sortedEntries = Array.from(highlightCache.entries())
+      .sort((a, b) => a[1].timestamp - b[1].timestamp)
+    const toRemove = sortedEntries.slice(0, highlightCache.size - MAX_CACHE_SIZE)
+    for (const [key] of toRemove) {
+      highlightCache.delete(key)
+    }
+  }
+}
+
 /**
  * Apply highlights to HTML content by injecting mark tags using DOM manipulation
  */
@@ -13,19 +61,24 @@ export function applyHighlightsToHTML(
     return html
   }
   
+  // Check cache
+  const cacheKey = getCacheKey(html, highlights, highlightStyle)
+  const cached = highlightCache.get(cacheKey)
+  if (cached && Date.now() - cached.timestamp < CACHE_TTL) {
+    return cached.html
+  }
+  
+  // Clean up cache periodically
+  cleanupCache()
   
   const tempDiv = document.createElement('div')
   tempDiv.innerHTML = html
   
-  // CRITICAL: Remove any existing highlight marks to start with clean HTML
-  // This prevents old broken highlights from corrupting the new rendering
-  const existingMarks = tempDiv.querySelectorAll('mark[data-highlight-id]')
-  existingMarks.forEach(mark => {
-    // Replace the mark with its text content
-    const textNode = document.createTextNode(mark.textContent || '')
-    mark.parentNode?.replaceChild(textNode, mark)
-  })
-  
+  // Collect all text nodes once before processing highlights (performance optimization)
+  const walker = document.createTreeWalker(tempDiv, NodeFilter.SHOW_TEXT, null)
+  const textNodes: Text[] = []
+  let node: Node | null
+  while ((node = walker.nextNode())) textNodes.push(node as Text)
   
   for (const highlight of highlights) {
     const searchText = highlight.content.trim()
@@ -34,14 +87,6 @@ export function applyHighlightsToHTML(
       continue
     }
     
-    
-    // Collect all text nodes
-    const walker = document.createTreeWalker(tempDiv, NodeFilter.SHOW_TEXT, null)
-    const textNodes: Text[] = []
-    let node: Node | null
-    while ((node = walker.nextNode())) textNodes.push(node as Text)
-    
-    
     // Try exact match first, then normalized match
     const found = tryMarkInTextNodes(textNodes, searchText, highlight, false, highlightStyle) ||
                   tryMarkInTextNodes(textNodes, searchText, highlight, true, highlightStyle)
@@ -51,7 +96,14 @@ export function applyHighlightsToHTML(
     }
   }
   
+  const result = tempDiv.innerHTML
   
-  return tempDiv.innerHTML
+  // Store in cache
+  highlightCache.set(cacheKey, {
+    html: result,
+    timestamp: Date.now()
+  })
+  
+  return result
 }