User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:99.0) Gecko/20100101 Firefox/99.0

Steps to reproduce:

run "GTK_USE_PORTAL=1 firefox"
save image (right click "Save Link As...")
save in a folder with 1000+ images

Actual results:

firefox freezes for less than a second, as you save more images to the same directory (I tried around 10) the freeze gets longer (up to 1 second).

Expected results:

firefox doesn't freeze when saving the image (works on Brave and Firefox on Windows).
Note that the said folder is on a 5400RPM HDD, but other browsers and operating systems didn't have this problem

Firefox Version: 99.0.1
Operating System: Arch Linux
KDE Plasma Version: 5.24.4
KDE Frameworks Version: 5.93.0
Qt Version: 5.15.3
Kernel Version: 5.17.3-zen1-1-zen (64-bit)
Graphics Platform: X11
Processors: 16 × AMD Ryzen 7 5800X 8-Core Processor
Memory: 15.6 GiB of RAM
Graphics Processor: AMD Radeon RX 580 Series

The Bugbug bot thinks this bug should belong to the 'Core::Performance' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Sounds like a Linux file IO specific issue.

The Performance Priority Calculator has determined this bug's performance priority to be P3. If you'd like to request re-triage, you can reset the Performance flag to "?" or needinfo the triage sheriff.

Impact on browser UI: Causes noticeable jank
Configuration: Rare