Adding, searching for, and synchronizing subtitles on online HTML5 videos. It is catalogued under Subtitles & captions on PulseGate.

+Sub is a consumer product built for firefox users who watch online videos.

What platforms does +Sub run on?

+Sub runs on the web and embeddable surfaces.

Is +Sub still active?

Unverified. +Sub has not been re-checked since it entered the index, so there is no finding either way — and only a positive finding would say otherwise.

What projects are similar to +Sub?

Similar projects tracked by PulseGate include Add Subtitles, Subs Translate, and Subtitle Speaker.

+Sub is developed by Stefan Breitenstein.

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+Sub

Name: +Sub
Author: Stefan Breitenstein

mozilla.orgSubtitles & captions

+Sub is a Firefox browser extension that adds subtitles to HTML5 videos from local files or online searches. It supports SRT, VTT, ASS, and SSA formats, synchronization offsets, transcript navigation, and embedded videos on services such as YouTube and Netflix.

FreeMITWebEmbeddable

Visit mozilla.org

58stars

14forks

10features

2016since

Overview

10 features

+Sub is a Subtitles & captions project. Adding, searching for, and synchronizing subtitles on online HTML5 videos. +Sub is a consumer product aimed at firefox users who watch online videos. +Sub is free to use. It ships for the web and embeddable surfaces.

Behind +Sub is Stefan Breitenstein, and it first shipped in 2016. Development happens publicly on GitHub with 58 stars. Key capabilities include subtitle search, local subtitle files, and subtitle synchronization. The interface is available in 32 languages, including Czech, German, and Greek.

Summary written by a language model from the project’s public pages.

Subtitle search
Local subtitle files
Subtitle synchronization
Transcript view
Transcript navigation
SRT support
VTT support
ASS support
SSA support
Iframe support

Built with & integrations

Framework

Vue

Connectors

github

Runs on

BrowserEmbeddable

Trust & compliance

License

MIT

Verified signals

HTTPSPrivacy Policy Terms of ServiceFree tierGitHub · ★ 58Multi-languageStore-verified publisher

Legal

Indexing history

What PulseGate has recorded for this listing

Indexed9 Sept · 16:18 UTC
+Sub verified via Firefox Add-ons
Source: Firefox Add-ons · Open

Frequently asked questions about +Sub

What is +Sub?: Adding, searching for, and synchronizing subtitles on online HTML5 videos. It is catalogued under Subtitles & captions on PulseGate.
Who should use +Sub?: +Sub is a consumer product built for firefox users who watch online videos.
Is +Sub free?: Yes — +Sub is free to use.
What platforms does +Sub run on?: +Sub runs on the web and embeddable surfaces.
Is +Sub still active?: Unverified. +Sub has not been re-checked since it entered the index, so there is no finding either way — and only a positive finding would say otherwise.
What projects are similar to +Sub?: Similar projects tracked by PulseGate include Add Subtitles, Subs Translate, and Subtitle Speaker.Add Subtitles Subs Translate Subtitle Speaker
Who develops +Sub?: +Sub is developed by Stefan Breitenstein.
How long has +Sub been around?: +Sub first shipped in 2016.

At a glance

Pricing: Free
Platforms: Web
Open source: Yes · ★ 58
License: MIT
First seen: 9 Sept 2026
Built for: Firefox users who watch online videos
Model: B2C
Solves: Adding, searching for, and synchronizing subtitles on online HTML5 videos.

Registered as

GitHub: plussub/plussub
Firefox Add-ons: plussub

Developer

Stefan Breitenstein

Small team

GitHub

Open source

View on GitHub

Stars: 58
Forks: 14
Open issues: 24
Last commit: 29 Jul 2024
Commits 90d: 0
Contributors: 3
Authorship: Small team
Default branch: master

Index record

Indexed: 9 Sept 2026
Lifecycle: Alive
First seen: Sept 2026
Last seen: 9 Sept 2026

Identity audit (13)

Slug: sub-mozilla-org
Lifecycle state recorded: 9 Sept 2026
Verification state: Indexed for public listing
Listing state: Listed: yes
Index status: Included in index
Latest evidence snapshot: 9 Sept 2026
Timeline basis: Indexed-at chronology (no inferred launch/funding milestones).
Name from: Derived from the project's own page and URL.
Category from: Assigned by a language model.
Summary from: Written by a language model from public pages.
Languages from: Detected by a language model, checked against the page's own declaration.
Last updated: 9 Sept 2026
Canonical URL: https://addons.mozilla.org/en-US/firefox/addon/plussub

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