Falkon (previously known as "QupZilla") is a web browser built on the Qt framework. It uses Qt's WebEngine (=chromium) for rendering. It supports themes, python plugins and filtering of unwanted elements. It has a lot of potential. It has some very fundamental usability problems which rules out using it as a daily browser. It could become an alternative to Firefox and Chrome/Chromium. As of now it's just not.
Features and usability
Falkon has the potential to be a great web browser and a viable alternative to Firefox and Chromium on the Linux desktop. It's just not there (yet).
Trying Falkon as the primary web browser for just a few hours reveals quite a few glitches and usability problems. If a site has too small text for your taste and you press
+ to make it bigger it does become bigger. Open a link from that site in a new tab or window and you get.. it's original text size. Other browsers will use the text-size you've set in same-site links opened in tabs or new windows. This is a common complaint known as bug #391438.
There's also an issue with the mousewheel randomly not working. You browse around and all is well and you scroll the mousewheel to read further in an article and you can't because the mouse wheel doesn't work.. Scrolling with the scrollbar or keyboard arrows will still work when this happens. This glitch happens too frequently to not be annoying.
The "speed dial" view you get when you open a new tab is really slow and sluggish even on top-notch computers. There is nothing "speedy" about it. Opening a blank tab should not put high load on the CPU (just one core, anyway) and take about as long as it takes to have a sip from a cup of tea.
Falkon does come with a AdBlock extension and it is configurable. The user-interface for managing it is far from user-friendly compared to uBlock Origin but it does let you do the most important tasks: Subscribe to filter lists and add custom rules.
While we could go on listing issues like these all day we expect you've already an idea of why our verdict is that Falkon simply does not provide a smooth enough experience to be a viable web browser alternative. Qt's WebEngine is sound when it comes to rendering pages correctly. Falkon has great potential and could, with a lot of work and effort, become a real challenger to Mozilla and Chromium on the Linux desktop. For now it's not.
Falkon's git version (3.1.99) supports plugins including Python-based plugins. There is already a Falkon category at store.kde.org with some extensions. The Python-ones require Shiboken2 and PySide2 which isn't part of many distributions so you may have a hard time using those extensions even if you build the Falkon git version. Your luck may vary.
The sluggish speed-dial issue described above appears to be fixed in the git version. The other problems are not.