SUMMARY Compiling git master falkon, I ran cmake, as one must, but then I decided I wanted to install it into a non-standard directory (in my case /opt/falkon). So I ran (in "build" directory): cmake -DCMAKE_INSTALL_PREFIX=/opt/falkon .. make but when I ran that build of falkon I got the error: 'Library plugin "TabManager.so" not found' Some debugging led me to find that the problem is in the src/CMakeLists.txt which contains the line: set(FALKON_PLUGIN_PATH "${PLUGIN_PATH}" CACHE PATH "Default plugin search path") which is storing the previous value (/usr/local/lib/falkon) in a cmake cache file, so further runs of "cmake .." are not changing the value. I modified the line to read: set(FALKON_PLUGIN_PATH "${PLUGIN_PATH}") and that solved it for me. Another solution is to delete the build directory and wait for a full compile. SOFTWARE/OS VERSIONS Falkon git master as of 2020 Jan 1 Linux Fedora Core 30 - 32bit QtWebEngine version 5.12.5 Frameworks 5.64
I believe you also need to have runtime env vars like qt_plugin_path set to this new path. I already gave up on setting all this and I use kdesrc-build to do the hard work for me.