Optimize Chrome Extension Background Script

I will hand over my current background.js—the engine behind a Chrome-style browser extension. After a series of quick fixes it has become cluttered and sluggish, so I need a professional refactor that restores speed without altering any user-visible behaviour.

The single, overriding goal is faster execution. Most of the lag comes from DOM operations, so that section deserves particular attention. Memory use and readability are welcome side benefits, yet performance must drive every decision.

I built and maintain the project in Sublime Text; please keep the file format, indentation, and line endings friendly to that editor. No new build tools, transpilers, or external libraries are expected—just modern, vanilla JavaScript that drops straight back into the existing extension.

Deliverable
• One cleaned, commented background.js that behaves exactly like the original but runs noticeably faster, especially in its DOM-handling routines.

Add a brief comment block at the top outlining key optimisation choices so I can follow your reasoning. Once I can swap the file in and see identical visuals with snappier response, the job is done. Let me know your turnaround time and any quick questions, and we’ll get started.