Firefox extensions on Android

(NOTE TO SELF -- see further instructions here)

Yes, it's actually possible to install add-ons in Firefox for Android:

1. install Firefox Nightly from the Play Store (explanation)
2. follow these instructions to enable add-ons for Firefox Nightly
3. start installing add-ons:
   • list of officially recommended extensions
   • list of extensions whose authors claim compatibility
4. in the 3-dot menu, choose "Add-ons", confirm that the collection list appears, and click the "+" sign next to the desired add-on

Specific extensions I like to use:

• Android PDF.js — view PDFs directly in the browser