The last post on the topic was published almost a year ago, and mobile-config-firefox has seen some important changes since - the best way is to read through the tag list and start at 5.0.0_rc1, as 4.6.1 landed the main topic of the previous post.

Merged improvements

I think aside from about:mobile and better popups the most important change is that we can now ship different CSS for ESR and release, which really helps to address changes.

Since the last release, 5.1.0, in December 2025, we've landed some more small fixes and improvements, that will hopefully improve everybodies experience once released.

Vertical tabs?

This post, following tradition, is about something different, something not yet merged though: Supporting the native vertical tabs feature on mobile (somewhat).

Honestly, when I first tried the feature on mobile, I was underwhelmed. It did not work for me, which since I can't wrap my brain around vertical tabs on desktop either, is not too surprising. I was at some point closer to preparing an Merge Request (MR) hiding the option to turn on vertical tabs in Settings (about:preferences).

But since Danny kept insisting that the feature may be nice on mobile, and I figured I had to try, I've now submitted a MR that does not hide the feature, but instead attempts to make vertical tabs on mobile work:

The MR has some more details, including screenshots - go check and try it out and report back if you see room for improvement.

How to help test this?

You need to have git and make installed.

First clone my fork and checkout the branch feature/somewhat-support-vertical-tabs:

git clone https://gitlab.postmarketos.org/1peter10/mobile-config-firefox.git
git checkout feature/somewhat-support-vertical-tabs

Then install it:

sudo make install

for Firefox release.

To test with ESR, Beta, Nightly or Librewolf respectively run:

sudo make FIREFOX_DIR=/usr/lib/firefox-esr install 
sudo make FIREFOX_DIR=/usr/lib/firefox-beta install 
sudo make FIREFOX_DIR=/usr/lib/firefox-nightly install
sudo make FIREFOX_DIR=/usr/lib/librewolf install

Note that all these install methods only work for native distribution packages, not flatpak/snap etc., on Debian, the path may be /usr/share/... instead of /usr/lib/....

And that's it for today!

Want to get involved?

If you are interested in making Firefox work better on #LinuxMobile devices, make sure to take a look at the open issues!

If you need help getting started or run into problems, make sure to check the new docs, the README, or feel free to ask on Matrix or IRC or in the issue tracker!

Thank you for reading this!