When a script is overloaded with tasks or contains an error, it can cause delays. If you suspect a bug in the script or are unsure of its origin, utilize the "Stop script" button to halt it. Pressing the Continue button will allow the script to resume if a lengthy task is underway. Repeat this process as needed for the script to complete its execution.
Error Isolation
To verify that the issue lies with the JavaScript script in Firefox, activate safe mode.
Further Investigation:
Script Profiling
Based on the screenshot evidence, it appears that the problem does not stem from a Firefox extension, making safe mode ineffective. Video ads served by video egg may also contribute to loading delays.
Utilize Firebug's profiler to assess the performance of the specific video egg script.