It could read the cache on a startup. Go to Settings -> Privacy and security and find Your stored cookies, site data, and cache are currently using ??????? of disk space. How much is it? You can clear it from there and test the startup time.

Also try these options. see screenshot Try downloading Firefox from Mozilla and run it from the folder. Do not sign into your Firefox account and see if you have the same issue. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

What OS? What Desktop? X11 or Wayland?

Operating System: openSUSE Tumbleweed 20230710 KDE Plasma Version: 5.27.6 KDE Frameworks Version: 5.108.0 Qt Version: 5.15.10 Kernel Version: 6.3.9-1-default (64-bit) Graphics Platform: X11 Processors: 16 × AMD Ryzen 7 5825U with Radeon Graphics Memory: 62.1 GiB of RAM Graphics Processor: AMD Radeon Graphics Manufacturer: HP Product Name: HP ProBook 455 15.6 inch G9 Notebook PC

It could read the cache on a startup. Go to Settings -> Privacy and security and find Your stored cookies, site data, and cache are currently using ??????? of disk space. How much is it? You can clear it from there and test the startup time.

Did you mean that it "could not" read the cache? Well, I set up Firefox to delete cache when closed. So, it should not try to find cache when I open it. I also set up automatic deletion of cookies except for the sites I visit regularly.

I checked the amount of cache right after boot-up and it seems like there's no cache stored initially.

Also try these options. see screenshot Try downloading Firefox from Mozilla and run it from the folder. Do not sign into your Firefox account and see if you have the same issue. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release What OS? What Desktop? X11 or Wayland? Operating System: openSUSE Tumbleweed 20230710 KDE Plasma Version: 5.27.6 KDE Frameworks Version: 5.108.0 Qt Version: 5.15.10 Kernel Version: 6.3.9-1-default (64-bit) Graphics Platform: X11 Processors: 16 × AMD Ryzen 7 5825U with Radeon Graphics Memory: 62.1 GiB of RAM Graphics Processor: AMD Radeon Graphics Manufacturer: HP Product Name: HP ProBook 455 15.6 inch G9 Notebook PC

My operating system is Arch Linux. I run bspwm on X11 and Hyprland on Wayland.

As I already mentioned, a reinstall speeds up the boot-up process (less than a second). But whenever I keep running the browser normally, the problem comes back. I do need to sign into my Firefox accounts so that I can sync all of my devices. A freshly installed Firefox boots up very fast but that doesn't solve the problem I'm facing in my daily use.

The performance profile shows a DBus proxy timeout (25 seconds) while getting the system theme. Go to about:config and try changing widget.use-xdg-desktop-portal.settings = 0.

Is this a flatpak package installation?

Can you run a virtual machine or usb live stick to test? The below cmd will create a log file (firefox_debug.txt) to show what's happening when you run Firefox. strace -t -o firefox_debug.txt firefox &

I blame ---> bspwm. What happens in KDE or Gnome?

This user is having the same issue https://support.mozilla.org/en-US/questions/1417284 and he is running wm xmonad.

Thank you all for replying. The problem was with the xdg desktop portal. I had Hyprland installed along with "xdg-desktop-portal-hyprland", which in turn had "xdg-desktop-portal" as a dependency. I don't use Hyprland that much. So, I just uninstalled those two programs. Firefox now boots up instantly.