This doesn't make sense? What you mean avi files are too big to display? That sounds more like a video driver issue?

AV1 Image File Format (AVIF) is an open, royalty-free image file format specification for storing images or image sequences compressed with AV1 in the HEIF container format. https://en.wikipedia.org/wiki/AVIF

The AVI or Audio Video Interleave you misread as is a not related proprietary multimedia container format.

Do you mean the length of the filename?

Can you attach a screenshot?

• https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem
• use a compressed image type like PNG or JPG to save the screenshot