Firefox stutters when not set as default browser

[vorot93]

Firefox kept freezing on startup, opening preferences, interacting with address bar, etc.

Profiler output:
https://share.firefox.dev/2PhbAqx
Apparently freezes happened because of code responsible for checking default browser.

After setting Firefox as default browser the freezes went away.

After deleting ~/.config/mimeapps.list Firefox started freezing again.

nixos-unstable-small, Firefox 79, GNOME 3.36.4

[worldofpeace]

I should mention nixos-unstable-small is not a good choice for user of a graphical environment. This is because the tests that run in order for that channel to advance are much fewer, and while this makes it advance faster (and nixos-unstable can be frequently blocked), this means tests like the gnome3 tests could fail and the environment could be broken. Just thought I should mention this.

[rastertail]

I just recently started using NixOS and am running into the same issue, except it still occurs even when my default browser is set to Firefox.
Startup profile: https://share.firefox.dev/3eH4vLS
NixOS 20.09, Firefox 82.0.2, GNOME 3.36.5 (Wayland)

[worldofpeace]

Hmm, I'd have to hear from @vorot93 if that can be reproduced by them. Because that could easily now be a different issue from @vorot93 @Rytone

[worldofpeace]

Also, good that you specified the wayland session. I wonder what session @vorot93 was using.

Anyways, I will try to reproduce this with those versions.

[teto]

happens to me even on X. Firefox is set as my default browser but the checkbox is greyed out because my "configuration is mangered by [my] organization" (configured via home-manager) .

[cmr-a]

I have this issue as well (running on gnome3, both X11 and Wayland).

I found that when the freeze happens Firefox runs xdg-settings check default-web-browser firefox.desktop, and then it blocks for about 1 second waiting to read from the stdout pipe.

The code that does this check when running on Gnome is here.

The code only runs xdg-settings if Firefox is running as a snap, which is determined by checking if the SNAP_NAME env var is set to "firefox". I tried removing SNAP_NAME from the Firefox environment, and this stopped any calls being made to xdg-settings. This is one possible workaround but I don't know if it will break something else.

I tried setting "browser.shell.checkDefaultBrowser" to false in about:config, which should stop Firefox from performing the default browser check on startup. However, this did not seem to work. Possibly related #65679 .

I found that xdg-settings is calling xdg-mime, and this command is very slow on my system:

> time xdg-mime query default x-scheme-handler/http
firefox.desktop
xdg-mime query default x-scheme-handler/http  0.50s user 0.47s system 154% cpu 0.625 total

I enabled debug logging with XDG_UTILS_DEBUG_LEVEL=2, which shows xdg-mime is searching about 100 files, running grep on each one of them. This is probably why it is slow.

The first file searched is ~/.config/mimeapps.list, which on my system has no entries.

If you open Gnome3 Settings -> Default Applications, then change your default web browser to anything other than Firefox, then change it back to Firefox, entries will be added to ~/.config/mimeapps.list like this:

[Added Associations]
x-scheme-handler/http=firefox.desktop;
text/html=firefox.desktop;
application/xhtml+xml=firefox.desktop;
x-scheme-handler/https=firefox.desktop;

[Default Applications]
x-scheme-handler/http=firefox.desktop
text/html=firefox.desktop
application/xhtml+xml=firefox.desktop
x-scheme-handler/https=firefox.desktop

After doing this, xdg-mime completes in 0.01 seconds, and the freezes in Firefox are gone.

To reproduce this issue I suggest deleting ~/.config/mimeapps.list then checking how long xdg-mime query default x-scheme-handler/http takes to complete.