First of all, you need to download Firefox Nightly, which is essentially the alpha developer version.
Direct link: https://www.mozilla.org/en-GB/firefox/channel/desktop/
Google Play link: https://play.google.com/store/apps/details?id=org.mozilla.fenix
You then need to go to https://addons.mozilla.org/en-US/firefox/collections/, click "Log in to view your collections", create an account, and then create a new collection with a unique name. Search for all the add ons you want to use, and add them to your collection, BPIP included. Make a note of the unique name you gave the collection, and the 8 digit number in the URL.
Open your Firefox Nightly app, go to settings, scroll to the bottom and select "About Firefox Nightly", and tap the Firefox logo five times until you get a pop up saying "Debug menu enabled".
Go back to settings, scroll down to "Advanced" and select "Custom Add-on Collection".
Enter the 8 digit number from above in the "Collection owner (User ID)" field, and the name you gave your collection in the "Collection Name" field, and hit OK.
The app will apply the changes and then shut down.
Relaunch the app, go to add ons, and you will see all the add ons from your collection listed. Tap the plus sign next to each one to install.
I can confirm that the BPIP extension works just fine using the above steps.
I want to confirm that this is working like a charm. Thank you very much for this wonderful workaround. It's amazing. Out of smerit for a long time now, I hope someone will send from me stay safe all of you guys (and girls)!