My advice-
Download Spybot ( free- spyware and adware detection and removal) Run it. It will get rid of alot of the browser hijackers. Spybot
Run it.
Next- Download Lavasoft Adware ( free version) Lavasoft Adware
Run it.

You should have at least 2 spyware removal programs, because one will inevitably catch something the other doesn't.

Then, download "Hijack This "( browser start up programs)
It will bring up a log file of what programs r starting up when you boot up.
Hijack This

Run the program. Copy the log file in its entirety.

Now, go to this spyware forum, and start a new post, and copy your log file, from Hijack This program, and ask nicely if they will look at it, and the members will tell u if there's something funny in there that shouldn't be...
ONLY TAKE ADVICE from ADMIN, MODS, or SENIOR members !

spyware Help Forum

Good Luck !!

( Spybot Search & Destroy will block alot of spyware, adware from being installed, in addition to u being able to run it, and having it detect, and remove,
Lavasoft free version will not block, but when u run it, it will detect, and remove )
Both programs are free, and have periodic updates .

Also, Mozilla browser is not immune to hijacks, and other adwares.
Spyware Blaster is good for blocking active X based downloads.

Seems like alot of , but these 3 spyware programs are very small, and do not take up alot of space on your computer.