Hello
Yes you can make any image into one that is seamlessly tiling. Although FF will not do all the work for you. Unless you use one of the filters that duplicates your image and overlaps and blurs the edges of your image. This can work for some things but not all. To make an image into one that is truly seamless you need to do that in photoshop or some other editor that allows you to make those fixes.
Make sure your image is square.
Go to PS-filters-other-offset, input a value -300 and +300 for a 600 px square image.
This will put all of your edges into the interior so you can clearly see how your edges will match up. Then you do and use whatever you can to make those edges come together. Clone brush, blur, paint whatever tools you may use to help you come up with a result that is acceptable to you. When you are finished reverse the offset filter and your ready to apply further affects in FF.
I hope this helps.
at least 90 percent of all sensation is texture, even beyond the visual, with elements of noise, tone, gradients, interval and degree.