pdfにカラーテーマを適用し閲覧できるpdfリーダーです。
基本的にはfirefox標準のPDFリーダーと同じように機能しますがリーダーのツールバーにReader mode optionのアイコンが追加されており、これをクリックするとカラーテーマを選択できます。

注意点としては、firefoxのセキュリティ制限により拡張機能が実行されているタブでしかpdfを閲覧できず、pdfファイルを開くことで拡張機能を利用した閲覧ができるわけではありません。拡張機能のメニュー(もしくはツールバーにピン留めされたアイコン)から拡張機能を開き、PDFをドラッグ&ドロップで開く必要があります。

ただ、これはあくまでfirefoxの制限による仕様ですので、不便ではありますが仕方がないかなと思います。
十分に有用な拡張機能です。

Firefox is now my favorite PDF viewer thanks to this add-on. Thanks for working on it and for making it open-source!

Exactly what i looked for! Many thanks!!!

Thank you thank you

As good as it gets! This Add-On includes all needed elements to directly handle PDF documents available in the net.

Addendum:
An additional useful feature could be to have a look at the fonts which are used (and probably embedded) in the viewed PDF as in most standalone PDF viewers.

Far superior to the Adobe Acrobat Official which can't leave you alone to do what you planned on doing. (Read the document.) This is straightforward, what one expects, from a document viewer. Thanks much!

Can I just say awesome? I've tried 'Dark PDF' extensions before which are limited and finnicky at best. The benefit of customizable PDF rendering schemes which WORK to make it both dark AND readable, or beige/sepia, or back to white, packaged as a subtle built-in feature of the default PDF reader for the browser is amazing. Totally underrated and single-handedly makes me glad to be using Firefox over Chrome.

Extremely helpful & awesome extensions.

It's a great extension, thank you so much!, I was searching for this long time ago!, thank again!

aww thank you so much for this! i have like a hundred scihub tabs and i'm kinda too lazy to have to download them all so this is a total lifesaver (and eyesaver ^^)
i'd like to ask if there's a way to make the reader itself dark mode, like normal firefox's?

I love it! thank you so much for making this extension!