[Performance Issue] Gmail attachments load extremely slowly with Dark Reader #16135

Prerequisites

• I searched for any existing report about this performance issue to avoid opening a duplicate.
• I have restarted the web browser to check if that resolved this performance issue.
• I can reproduce this performance issue in a new, unmodified web browser profile with Dark Reader installed as the only extension.

Performance Issue Description

Whenever I attempt to preview any attachments (docx, pdf, png) in Gmail with Dark Reader enabled, they load extremely slowly and also slow down the current tab. Regardless of how small or large the attachment is, it takes around 10-20 seconds both for the attachment to fully load and for the lag to disappear.

This started around 2 weeks ago when Gmail appeared to start using a new renderer for attachments. I have already tried clearing my browser's cookies and updating all of my device's software (along with obvious things like restart my browser/computer), and these produced no noticeable difference.

Website Address

https://mail.google.com/mail/u/0/?shva=inbox#inbox

Steps To Reproduce

1. Install Dark Reader on Firefox
2. Enable it for mail.google.com
3. Attempt to preview any attachment from an email directly in Gmail without downloading it.

Performance Profile

Firefox 2026-10-23 16.32 profile.json.gz

Screenshots

No response

Operating System

Fedora Linux 43 (Workstation Edition)

Web Browser name and version

Firefox 157.0.1 (64-bit)

Dark Reader version

4.9.133

Does this happen when Dark Reader is disabled?

No

Does this happen in other web browsers?

Yes

Additional Context

I've briefly attempted to replicate this issue in Google Chrome 156.0.8078.47 (Official Build) (x86_64) and the issue persisted, though my attachments did take less time to load in Chrome.