One thing you may wish to try is to search directly for extensions from the Extensions panel rather than from ‘Get Add-ons’. I found this works better for some reason. (This also cuts down on the all the extraneous add-on information one must navigate on Mozilla’s site.) To be clear: From the ‘Open menu’ stack icon, select Add-ons->Extensions and use the ‘Search all add-ons’ box in the upper right.
I installed uBlock Origin and uMatrix this way, in addition to a few other privacy add-ons.
thanks for the trick. In my case this box seems to be just a link to Mozilla’s site. It’s not called ‘Search all add-ons’ here, it’s called ‘Search on addons.mozilla.org’ and whatever I type in there gets searched on a newly opened page that brings me back to Mozilla’s site.
The way I install add ons is that I sync my PureBrowser with my firefox. So when I install an addon on Firefox on another machine, then the addon appears in PureBrowser. Not very practical.
I suspect things have changed since I posted this. I actually stopped using PureBrowser, so I cannot try or look at anything.
If you have not tried it yet, @mladen later posted a work-around that might make adding extensions easier. It is at the bottom of his “Firefox Compat Mode” fix page here. Maybe it will help.
Also, a handful of the more popular privacy-related add-ons are in ‘green,’ e.g. uBlock Origin, uMatrix, HTTPS Everywhere, and Privacy Badger. Be careful, however. I found, at the time, those interfered with my Quantum installation on PureOS. (I did not try hard to debug this; I eventually just uninstalled the webexts and PureBrowser.)