For whatever reason Steam Deck pretty much has two default browsers: Google Chrome in Game Mode and Firefox in Plasma aka. Desktop Mode. Firefox is absolutely unusable in Game Mode. Chrome (probably most other Chromium variants as well, I’ve only tried a handful) work okay-ish – at least they don’t go ballistic on touch events but they are not a truly nice experience either.
Readers of Planet KDE probably already know that some KDE applications have convergent GUIs thanks to Plasma Mobile, including the Angelfish web browser. It took some fiddling but after a while I managed to get it into a shape that’s very usable in Game Mode. Without any tweaks Angelfish defaults to use its desktop GUI and thereby runs just fine in Plasma Desktop, perhaps docked to a monitor.
First step is to enter Desktop Mode and install Angelfish from Flathub via Discover and then add it to Steam.
Then within Steam under Properties of Angelfish add this in the Target line to the beginning of the command to force mobile user interface, loading icons, and enlarging the interface elements:
env QT_QUICK_CONTROLS_MOBILE=1 QT_QPA_PLATFORMTHEME=KDE QT_SCALE_FACTOR=2
Next step is to enter Game Mode and select the Web Browser controller layout:
Here’s a few screenshots of Angelfish running:
In all fairness, Angelfish is a bit barebones. The Chromium-derived rendering engine is fine but there is no way to sync bookmarks and passwords with other browsers or at least import them. An ad blocker is built in but there’s also no support for WebExtensions or User Scripts, as far as I can tell. Keyboard does not automatically pop up on text inputs, you’ll need to press X every time. Despite all the downsides, it’s miles ahead of using a desktop-focused browser in Game Mode. You can also just launch Angelfish from Plasma Desktop without the above tweaks and just continue to use the same tabs, sessions, etc.
I can’t speak for the Plasma Mobile team but I hope they’ll embrace platforms like Steam Deck to lure in a few new contributors. Many of the other Plasma Mobile apps look potentially useful on handheld PC platforms as well.
PS: Angelfish also has a tablet UI that you can enable by replacing QT_QUICK_CONTROLS_MOBILE with KDE_KIRIGAMI_TABLET_MODE but I did not find it particularly working well with Game Mode.