Tables with large cell contents using colspan and rowspan are not exported properly in Firefox when using User Browser as generator if Header and/or Footer is selected

Steps to reproduce

1. Open XWiki on Firefox (tested with Firefox 148.0.2)
2. Create a page with the following content:

   |=Group|=Subgroup|=Item
   |(% colspan="1" rowspan="40" %)Group 1|(% colspan="1" rowspan="20" %)Subgroup 1|Item 1
   |Item 2
   |Item 3
   |Item 4
   |Item 5
   |Item 6
   |Item 7
   |Item 8
   |Item 9
   |Item 10
   |Item 11
   |Item 12
   |Item 13
   |Item 14
   |Item 15
   |Item 16
   |Item 17
   |Item 18
   |Item 19
   |Item 20
   |(% colspan="1" rowspan="20" %)Subgroup 2|Item 1
   |Item 2
   |Item 3
   |Item 4
   |Item 5
   |Item 6
   |Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.  Item 7 is really long.
   |Item 8
   |Item 9
   |Item 10
   |Item 11
   |Item 12
   |Item 13
   |Item 14
   |Item 15
   |Item 16
   |Item 17
   |Item 18
   |Item 19
   |Item 20
   |(% colspan="1" rowspan="40" %)Group 2|(% colspan="1" rowspan="20" %)Subgroup 1|Item 1
   |Item 2
   |Item 3
   |Item 4
   |Item 5
   |Item 6
   |Item 7
   |Item 8
   |Item 9
   |Item 10
   |Item 11
   |Item 12
   |Item 13
   |Item 14
   |Item 15
   |Item 16
   |Item 17
   |Item 18
   |Item 19
   |Item 20
   |(% colspan="1" rowspan="20" %)Subgroup 2|Item 1
   |Item 2
   |Item 3
   |Item 4
   |Item 5
   |Item 6
   |Item 7
   |Item 8
   |Item 9
   |Item 10
   |Item 11
   |Item 12
   |Item 13
   |Item 14
   |Item 15
   |Item 16
   |Item 17
   |Item 18
   |Item 19
   |Item 20
   

3. Click More Actions > Export > PDF > Export
4. Keep all PDF Export Options ticked
5. Click Export
6. Observe the exported PDF

Expected results

The cell with large content is displayed with normal width.

Actual results

The large cell is displayed very narrow.

This doesn't reproduce if Footer and/or Header are not ticked (please see the attached screenshots).

The issue was reproduced also on XWIki 18.2.0 SNAPSHOT.

I've tested on Debian 12 VM with Firefox 148.0.2 and I could reproduce the issue there as well.

Also, npetrenko tested on his Ubuntu 24.04.4 machine and could reproduce it.