Subtitle Line Spacing Issue in Jellyfin on Firefox

[rbrglez]

I’m experiencing an issue with subtitles while using Jellyfin. When I connect to Jellyfin via the web GUI using Firefox and play a movie, I notice that there is a large gap between subtitle lines. However, when I check the subtitle settings in Jellyfin, I don't find any option to adjust the spacing between lines.
Interestingly, when I use the subtitle preview feature in the settings, the line spacing looks normal. This issue seems to be isolated to Firefox, as I tested the same scenario in Chrome, and the subtitles display correctly without the large gap.
I've attached screenshots comparing the same scene in both Firefox and Chrome for reference.

Screenshots:

1. Firefox subtitles
   
2. Chrome subtitles
   

System Information:

• Firefox Version: 131.0.3 (64-bit)
  
• Chrome Version: 130.0.6723.58 (Official Build) (64-bit)
  
• Jellyfin Version: 10.9.11
  
• Operating System: Pop!_OS 22.04 LTS
  

Has anyone else encountered this issue? Any suggestions for a fix or workaround would be appreciated!
Thanks in advance!

[Fate]

what subtitle format are we talking about? srt?

[rbrglez]

yes, subtitle format is *.srt
I didn't try with any other format.

[TheDreadPirate]

When using SRT subtitles, the client device is 100% responsible for rendering the subs. In this case, Firefox and Chrome. Jellyfin is 0% involved beyond sending the client the subtitle track. In my experience, Firefox is pretty terrible with subtitles and other users have reported similar issues. Also on Firefox.