Try <Ctrl>+ (ie, pressing the + key while holding down the <Ctrl> key). I think it works on most PCs and PC OSs. On my Linux PC, it remembers for the website too, so whether or how much I increase the size for a particular site is remembered, independently of other sites' size.
The ctrl + works great. On my laptop the + is the upper case = so you'll actually use ctrl shft + to increase and ctrl - to decrease.
I cannot afford to misplace my glasses because I'll never be able to find them without my glasses.