The first issue (button FIRST), there was conflict with the style in the flex template: templates/flex/css/template.css, templates/flex/css/presets/preset1.css
The second issue (first, last, next and prev), you can replace
COM_JAMEGAFILTER_NEXT (~ line 41),
COM_JAMEGAFILTER_PREV (~ line 27) in plugins/jamegafilter/virtuemart/layouts/default/product-toolbar.php .
Then add 2 lines below into language/en-GB/en-GB.com_jamegafilter.ini and translate it to your language:
The thir issue (arrow up & down), there seems to be a conflict too and I need more time to optimize it.
Please check again and let me know.