It does what is advertised but is far from flawless. For anyone that doesn't know Firefox lets you choose how you want to open pdf files, which makes this extension useless.

Go to Settings > General.
Scroll down to the Applications section and find Portable Document Format (PDF).
In the Action column next to it, choose Open with [Your PDF Viewer] or Always ask.

Очень удобное для работы расширение

Good add but works a bit slow

This is amazing, It's totally what I need. The plugin is highly compatible with PDF reader "zathura", which could open PDF from remote url without downloading it. Since I need to view a lot of PDF files, I am always finding a perfect solution for examing online PDF files efficiently. Combine this plugin with the other plugin "Vimium C" and PDF reader "zathura" (which is also Vim-like), I could browse PDF files from websites with only keyboard (without any clicking on mouse).

Buena, ya la he utilizado en otro dispositivo.

It does not open and does not work. Furthermore, it is "snoop" software that requires permissions that I do no with to grant.