I was using Weava for a long time, and in recent months I have been trying to change from Chrome to Firefox, and I couldn't find an alternative that would satisfy me.
Diigo was pretty good, but then I found out that I could only put a limited amount of PDFs into my library, which is very important for my work, and lucio got discontinued.
I want something which can work with both Web and PDFs, is cross-platform (desktop-Windows, Firefox and mobile-Android). Having to download additional software doesn't bother me.