I haven't seen this exact shape before but have seen many similar items offered by wholesalers & manufacturers in mainland China. Small teapots are a very popular gift & in addition to the traditional ceramic forms, there are a wealth of examples made in other materials, from carved hardstone to pressed glass and liu-li (pate-de-cristal). The seal mark is in stylised archaic script & very difficult to read, a sharper photo or perhaps a rubbing may help, but no guarantees. The best my wife & I can make out is that the bottom right character may be 'long' as in Qianlong but we cannot be certain at this point.
Mainland production is more likely than Taiwan, though Taiwan can not be ruled out. The mark does not appear in any of my Chinese catalogues but these are hardly an exhaustive resource as I was only able to contact wholesalers in Shanghai & Wenzhou. There are many small manufacturers of glass and other giftwares which have sprung up in the last 15 years, finding out who made what can be nigh on impossible, but this is one of the reasons I find Chinese glass so interesting. I would estimate that your teapot is likely to be recent, i.e. produced in the last 10 years. the colour is typical for for modern Chinese, this blue, along with a slightly dingy amber appears very frequently.